Name: Mary Berry Mars Bar Cake Recipe
Prep time: 20 min
Cook time: 10 min
Total time: 1 h 30 min
Ingredients: 4 Mars Bars standard size roughly 58g each, chopped into small pieces; 100g unsalted butter, cut into cubes; 3 tablespoons golden syrup; 90g Rice Krispies; 200g milk chocolate, broken into pieces; 30g unsalted butter, cut into cubes

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This Mars Bar cake is a dense, fudgy traybake with a deep caramel-chocolate flavour running through every layer. The base is chewy and slightly crisp at the edges, pressed through with Rice Krispies that keep a gentle crunch even after the chocolate topping sets to a smooth, glossy finish. It needs no oven, no eggs, and no complicated technique, making it a reliable choice for bake sales, birthday parties, or weekend treats with the children. From start to finish, including setting time, it is ready in around 1 hour 30 minutes.

What sets this version apart is the balance between the buttery Mars Bar mixture and the milk chocolate topping. Too often the topping is rushed and ends up streaky. Here the proportions are straightforward and the steps keep everything smooth and well-structured.

Ingredients

For the base

4 Mars Bars (standard size, roughly 58g each), chopped into small pieces
100g unsalted butter, cut into cubes
3 tablespoons golden syrup
90g Rice Krispies

For the topping

200g milk chocolate, broken into pieces
30g unsalted butter, cut into cubes

How to Make Mary Berry Mars Bar Cake Recipe

Prepare the tin: Line a 20cm square baking tin with non-stick baking parchment, pressing the paper into the corners and leaving an overhang on two sides so the finished slab lifts out cleanly.
Melt the base mixture: Place the chopped Mars Bars, 100g of butter, and golden syrup into a medium heavy-based saucepan over a low heat. Stir continuously with a wooden spoon until everything has melted into a smooth, amber-coloured liquid, then immediately remove from the heat so the mixture does not begin to bubble and separate.
Fold in the Rice Krispies: Tip all the Rice Krispies into the saucepan and stir quickly to coat every piece in the caramel mixture. Work fast here, as the mixture begins to firm as it cools and an uneven coat will give a crumbly base rather than a cohesive slab.
Press into the tin: Pour the cereal mixture into the prepared tin and use the back of a lightly oiled spoon or a piece of greaseproof paper to press it down into a firm, even layer reaching all four corners. Set aside while the topping is prepared.
Make the chocolate topping: Melt the milk chocolate and 30g of butter together in a heatproof bowl set over a pan of barely simmering water, stirring gently until the mixture is glossy and completely smooth. The water must not touch the base of the bowl, otherwise the chocolate can turn grainy and dull.
Pour and spread the topping: Pour the melted chocolate mixture over the pressed base and use a palette knife or the back of a spoon to spread it into an even layer that reaches the edges. Tap the tin gently on the worktop once or twice to level any ridges.
Set in the fridge: Transfer the tin to the fridge and leave for at least 1 hour until the chocolate topping is fully set and firm to the touch. Avoid the freezer for quick-setting, as this can cause the chocolate to bloom and develop a whitish, dull surface.
Slice and serve: Lift the slab out using the parchment overhang and place on a chopping board. Use a large sharp knife warmed briefly under hot water and wiped dry to cut clean squares. A warm blade slices through the set chocolate without cracking it.

Tips for the Best Mary Berry Mars Bar Cake

Why is my base crumbling apart when I try to slice it?

The mixture was most likely not pressed firmly enough into the tin, or the Rice Krispies were not fully coated before spreading. Use a flat-bottomed glass or the back of a metal spoon to compact the base with firm, even pressure before the topping goes on.

Why has my chocolate topping gone dull and streaky after setting?

This is usually caused by overheating the chocolate or by moisture getting into the bowl during melting. Keep the heat low and ensure no steam rises into the bowl. A gentle stir rather than vigorous beating also keeps the finish smooth.

Why is my Mars Bar mixture grainy instead of smooth?

Graininess occurs when the heat is too high and the nougat in the Mars Bars begins to separate rather than melt evenly. Keep the hob on the lowest setting and stir constantly, removing the pan from the heat as soon as the last piece has dissolved.

Why does the chocolate crack when I cut the slices?

A cold or thin chocolate layer cracks under a cold knife. Warm your knife under hot running water, wipe it dry, and cut with one firm downward motion rather than a sawing action. The warm blade melts slightly through the chocolate rather than forcing it apart.

Why is my base too soft even after an hour in the fridge?

This can happen if the golden syrup quantity was slightly over-measured or if the base was not pressed down tightly enough. Return it to the fridge for a further 30 minutes, and next time measure the golden syrup with a warmed spoon for a more accurate pour.

Serving Suggestions

Serve the squares at room temperature so the caramel layer softens slightly and the flavour is at its fullest rather than hard and cold from the fridge.
Cut into smaller rectangles for a children’s party plate alongside satsumas and plain biscuits to balance the richness.
Pair with a strong mug of Yorkshire tea, where the tannins cut through the sweetness of the chocolate topping.
Arrange on a slate board with a light dusting of cocoa powder for a simple but tidy presentation at a bake sale table.
Crumble one square over a bowl of good vanilla ice cream for a quick, indulgent dessert that comes together in minutes.

Storage

Room temperature

Store the cut squares in a single layer in an airtight container at room temperature for up to 2 days, keeping the container away from direct sunlight or any heat source.

Refrigerator

Place the squares between sheets of baking parchment in an airtight container and refrigerate for up to 5 days. Remove them from the fridge at least 20 minutes before serving so the caramel layer softens back to its proper chewy texture rather than being hard and dense.

Freezing

Wrap individual squares tightly in cling film and place in a zip-lock freezer bag, then freeze for up to 2 months. Defrost overnight in the fridge and leave at room temperature for 30 minutes before eating so the texture returns to its original state.

Nutrition

Calories: 290 kcal
Carbohydrates: 38g
Protein: 3g
Fat: 14g
Saturated Fat: 8g
Sodium: 95mg

Nutrition values are estimates and will vary depending on the specific brands of chocolate and Mars Bars used, as well as the portion size cut.

FAQs

Can I use dark chocolate instead of milk chocolate for the topping?

Dark chocolate works well if a less sweet finish is preferred. Use one with around 50 to 60 percent cocoa solids rather than a very high percentage, as a strongly bitter topping can clash with the sweet caramel base rather than complement it.

Can I make this Mars Bar cake a day ahead?

Yes, and in fact it slices more cleanly when made the day before. Cover the tin with cling film after the chocolate has set and refrigerate overnight, then cut and plate just before serving.

Can I use a different cereal instead of Rice Krispies?

Cornflakes or puffed wheat can be used in place of Rice Krispies and give a slightly different texture. Cornflakes produce a crispier, flatter bite while puffed wheat stays softer. Avoid granola, as the clusters do not mix evenly through the caramel.

What size tin works best for this recipe?

A 20cm square tin gives squares of a good thickness, around 2 to 2.5cm once topped. A larger tin such as a 23cm square will produce a thinner traybake that sets faster but has less chew in the base.

Can I double this recipe for a larger batch?

The recipe doubles straightforwardly. Use a 30 by 20cm rectangular tin and allow an extra 20 to 30 minutes of setting time in the fridge, as the thicker base and topping take longer to firm all the way through.

Conclusion

This Mary Berry Mars Bar cake recipe is one of the most straightforward no-bake traybakes to keep in your repertoire. The caramel base comes together in a single saucepan in under ten minutes, the milk chocolate topping sets to a clean, glossy finish, and the result cuts into neat, fudgy squares that hold their shape without crumbling. Made in a 20cm square tin, this recipe yields approximately 16 squares, depending on how thickly they are cut.

Whether made for a school bake sale, a birthday gathering, or simply a midweek treat, this traybake delivers consistent results every time without any specialist equipment. If you try this recipe, leave a comment below to share how it turned out, or share the page with a friend who enjoys no-bake baking. If you enjoyed this, you might also like the Mary Berry Apple and Cinnamon Cake Recipe for a classic oven-baked option with warm spice and tender crumb.