Name: Mary Berry Leek And Potato Gratin Recipe
Prep time: 20 min
Cook time: 55 min
Total time: 1 h 15 min
Ingredients: 700g floury potatoes, peeled and thinly sliced (about 3mm); 2 large leeks, trimmed, washed and cut into 1cm rounds; 1 small onion, halved and finely sliced; 2 garlic cloves, finely crushed; 25g unsalted butter; 1 tbsp olive oil; 250ml double cream; 150ml whole milk; 1 tsp Dijon mustard; 1/2 tsp freshly grated nutmeg; 1/2 tsp fine sea salt; a few grinds of black pepper; 4 fresh thyme sprigs, leaves stripped; 75g mature Cheddar cheese, coarsely grated; 25g Parmesan or Grana Padano, finely grated; softened butter for greasing the dish

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This leek and potato gratin is a layered, golden-topped bake with tender potato slices cushioned between silky, cream-soaked leeks and a bubbling, lightly browned cheese crust. The cut through the gratin reveals distinct layers, each one fragrant with thyme and warm with a gentle richness that is deeply satisfying without being heavy.

What sets this version apart is its reliability. The proportions are carefully balanced so the cream sets into a smooth, cohesive sauce rather than pooling at the base, and the leeks are given time to soften properly before the dish goes into the oven. It suits a midweek supper beside roast chicken, but is equally at home on the table at a relaxed weekend gathering. From start to finish, it is ready in around 1 hour 15 minutes.

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Ingredients

For The Gratin Base

700g floury potatoes, peeled and thinly sliced (about 3mm)

2 large leeks, trimmed, washed and cut into 1cm rounds

1 small onion, halved and finely sliced

2 garlic cloves, finely crushed

25g unsalted butter

1 tbsp olive oil

For The Cream Sauce

250ml double cream

150ml whole milk

1 tsp Dijon mustard

1/2 tsp freshly grated nutmeg

1/2 tsp fine sea salt

A few grinds of black pepper

4 fresh thyme sprigs, leaves stripped

For The Topping

75g mature Cheddar cheese, coarsely grated

25g Parmesan or Grana Padano, finely grated

Softened butter, for greasing the dish

How to Make Mary Berry Leek And Potato Gratin

Prepare the dish and preheat the oven

Heat the oven to 180°C (160°C fan, Gas 4). Rub a shallow 1.5-litre ovenproof baking dish generously with softened butter, making sure to coat the sides as well as the base. This prevents the cream from sticking and helps the edges of the gratin turn golden rather than pale.

Soften the leeks and onion

Melt the butter with the olive oil in a wide frying pan over a medium-low heat. Add the sliced leeks, onion and garlic, and cook gently for 8 to 10 minutes, stirring occasionally, until the leeks are soft and collapsed but not coloured. Pre-cooking the leeks ensures they release their moisture in the pan rather than making the gratin watery in the oven.

Mix the cream sauce

Combine the double cream, milk, Dijon mustard, nutmeg, thyme leaves, salt and black pepper in a jug and stir well. Taste and adjust the seasoning if needed. Set the jug aside.

Layer the potato and leek mixture

Arrange half the potato slices in a single, slightly overlapping layer across the base of the prepared dish. Spread the softened leek mixture evenly over the potatoes, then top with the remaining potato slices arranged in neat overlapping rows. Keeping the layers distinct means the cream sauce can flow through evenly, cooking the potatoes at the same rate throughout.

Pour over the cream sauce

Pour the cream mixture slowly and evenly over the layered potatoes, allowing it to settle between the slices. Give the dish a very gentle press with the back of a spoon to help the liquid reach the lower layers.

Add the cheese topping

Scatter the grated Cheddar and Parmesan evenly over the surface. The combination of the two cheeses gives a crust that is both stretchy and deeply savoury, with the Parmesan adding a nutty, slightly crisp finish.

Bake until golden and tender

Cover the dish loosely with foil and bake in the centre of the oven for 35 minutes. Remove the foil and continue to bake for a further 20 to 25 minutes until the top is deep golden brown and bubbling, and a sharp knife meets no resistance when inserted into the centre. If the cheese begins to darken too quickly before the potatoes are cooked through, re-cover loosely with foil for the remaining time.

Rest before serving

Remove the gratin from the oven and leave it to rest, uncovered, for 8 to 10 minutes before serving. Resting allows the cream sauce to settle and thicken slightly, so the portions hold their shape when spooned out rather than collapsing into a pool of liquid.

Tips for the Best Leek and Potato Gratin

01 Why is my gratin still watery after the full baking time?

The most common cause is leeks that were not cooked down properly before layering. Raw leeks release a significant amount of water in the oven, which dilutes the cream sauce and prevents it from setting. Make sure the leeks are fully softened and any excess liquid has evaporated from the pan before assembling the dish.

02 How do I stop the cheese topping from becoming too dark before the potatoes are cooked?

Re-cover the dish with a loose sheet of foil as soon as the cheese reaches a deep golden colour, then continue to bake until the potatoes are completely tender. Starting the bake covered for the first 35 minutes also helps protect the topping and allows the potatoes to steam through from below before the browning stage begins.

03 Why are my potato slices still firm in the middle even though the top looks done?

Potato slices that are too thick will not cook through in the allotted time. Aim for slices no thicker than 3mm, using a mandolin or a steady hand with a sharp knife. Floury varieties such as Maris Piper or King Edward also cook more evenly than waxy potatoes, which hold their shape but can remain firm in the centre of a gratin.

04 How do I get clean, neat portions when serving the gratin?

Resting the gratin for at least 8 to 10 minutes after it comes out of the oven is the key step. During resting, the cream sauce cools slightly and firms up around the layers, allowing a wide spatula or spoon to lift clean portions without the layers sliding apart. Serving directly from a hot oven always results in looser, messier portions.

05 Why does my cream sauce bubble over the edges of the dish during baking?

This usually happens if the dish is too small or filled right to the brim. Leave at least 2cm of space between the top of the layered potatoes and the rim of the dish before adding the cheese. Placing the baking dish on a foil-lined tray underneath also catches any overflow and keeps the oven clean.

Serving Suggestions

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Serve as a substantial side alongside a roasted leg of lamb or a slow-roasted shoulder of pork, where the richness of the gratin balances the lean, savoury meat.

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Pair with a simple crisp green salad dressed in a light sherry vinegar dressing to cut through the cream and add freshness to the plate.

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Spoon beside pan-seared trout or a fillet of salmon for a relaxed supper that feels a little more refined without requiring much extra effort.

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Bring to the table in its baking dish with a bunch of watercress on the side, which wilts slightly against the heat and adds a peppery contrast.

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Serve as the main course of a vegetarian meal, accompanied by steamed purple sprouting broccoli and a wedge of crusty sourdough to mop up the sauce.

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Storage

Up to 1 Day

Room Temperature

Store cooled leftovers in an airtight container at room temperature for up to one day, keeping the dish away from direct sunlight or heat sources.

Up to 3 Days

Refrigerator

Transfer the cooled gratin to an airtight container or cover the baking dish tightly with cling film and refrigerate for up to three days. To reheat, bring the gratin to room temperature for 20 minutes before placing it in a 180°C oven for 15 to 20 minutes until heated through and the cheese topping is bubbling again.

Up to 2 Months

Freezing

Wrap individual portions tightly in cling film and then in a layer of foil, or place in freezer-safe containers, and freeze for up to two months. Defrost thoroughly in the refrigerator overnight, then reheat covered in a 180°C oven for 25 minutes, removing the cover for the final 5 minutes to re-crisp the topping.

Nutrition

Calories

390

kcal per serving

28g

Carbohydrates

10g

Protein

27g

Fat

16g

Saturated Fat

360mg

Sodium

Nutrition values are estimates based on standard ingredient data and may vary depending on the specific brands used, portion size, and any ingredient substitutions made.

FAQs

Can I make the leek and potato gratin the day before and reheat it?

Yes, this gratin reheats very well. Assemble and bake it fully, allow it to cool, then cover and refrigerate overnight. Reheat in a 180°C oven for 20 to 25 minutes until piping hot all the way through. The texture of the cream sauce actually firms up slightly after resting overnight, which can make portions easier to serve.

Can I use crème fraîche instead of double cream in this gratin recipe?

Full-fat crème fraîche can replace double cream in equal quantities and gives a slightly tangier, less rich result. Avoid using half-fat crème fraîche as it is more likely to split during the long bake. If using crème fraîche, reduce the milk by about 30ml to account for its thicker consistency.

What type of potato works best in a leek and potato gratin?

Floury varieties such as Maris Piper or King Edward give the best results. They absorb the cream sauce and become yielding and soft in the centre while their surfaces turn lightly set at the edges. Waxy potatoes like Charlotte hold their shape too firmly, which means the layers can feel separate rather than cohesive after baking.

Can I leave out the cheese topping or use a different cheese?

The cheese topping can be left off entirely for a more delicate, cream-focused gratin. If you prefer a different cheese, Gruyère or Comté are excellent substitutes that melt smoothly and have a nutty depth. Red Leicester is another option for a slightly milder, more golden topping. Avoid soft cheeses such as Brie or cream cheese, which will not form a proper crust.

Can I double this recipe to feed a larger group?

Yes, the recipe doubles straightforwardly. Use two separate baking dishes of the same size rather than one very deep dish, as a single deep vessel will take significantly longer to cook through and the cream may not set evenly. Both dishes can be baked side by side on the same shelf or on two shelves, rotating them halfway through baking for an even colour.

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Conclusion

This Mary Berry leek and potato gratin is a dish that rewards patience and a little attention to detail. Pre-cooking the leeks, slicing the potatoes thinly and allowing the gratin to rest before serving are the three steps that make the real difference between a good result and an excellent one. The finished gratin has layered, tender potato held in a cream sauce that is set and silky rather than thin, with a cheese crust that is golden, bubbling and lightly crisp at the edges. This recipe serves 4 as a generous side dish or 2 to 3 as a main course.

If this became a favourite in your kitchen, leave a comment below to share how it turned out, or pass it on to someone who would enjoy it at their table. For another comforting, crowd-pleasing dinner idea, you might also like this Mary Berry beef stroganoff recipe, which is just as reliable and every bit as satisfying.