A decadent dessert featuring a crisp biscuit base topped with a rich, creamy chocolate mousse — perfect for sharing and impressive enough for guests.

Why You’ll Love This Recipe

This dessert combines textural contrast and deep chocolate flavour. The biscuit base gives a satisfying crunch, while the smooth mousse brings luxurious indulgence. It’s elegant yet approachable and makes a wonderful show-stopper after dinner.

Ingredients

For the Base
150 g digestive biscuits (crushed)
75 g unsalted butter (melted)
75 g dark chocolate chips

For the Mousse
2 medium eggs (separated)
150 g caster sugar
225 ml milk
2 sachets gelatine (equivalent to 6 teaspoons)
90 ml hot water (6 tablespoons)
150 g 72% extra dark chocolate (chopped)
5 ml Madagascan vanilla extract (1 teaspoon)
275 ml double cream

(Tip: You’ll find the full list of ingredients and measurements in the recipe card below.)

Directions

Pre-heat your preparation: line the base of a deep 20 cm (8 inch) square cake tin with foil.
Make the base: mix the crushed biscuits, melted butter and dark chocolate chips together. Press the mixture firmly into the base of the prepared tin using the back of a spoon. Chill until firm.
For the mousse: whisk the egg yolks with 75 g of the caster sugar in a bowl. Meanwhile, bring the milk to the boil. Pour the hot milk over the egg-yolk mixture slowly, whisking constantly. Return everything to the saucepan and heat gently until the mixture thickens slightly — however do not allow it to boil.
Dissolve the gelatine in the hot water. Then stir into the thickened milk-and-egg mixture along with the chopped dark chocolate and the vanilla extract. Stir until completely smooth and allow this mixture to cool slightly.
Whip the double cream lightly until soft peaks form, then fold it into the cooled chocolate mixture. In a separate clean bowl, whisk the two egg whites until stiff peaks form, adding the remaining sugar a spoonful at a time. Gently fold the egg whites into the chocolate-cream mixture.
Pour the mousse over the chilled biscuit base, smoothing the top. Return to the fridge and chill for about 2 hours to set.
Once set, cut into squares to serve. Optionally, serve with whipped cream and a dusting of cocoa powder.

Servings and timing

Serves: 9 people
Total time: Approximately 60 minutes preparation + chilling time (about 2 hours)

Variations

Use milk chocolate or white chocolate instead of 72% dark for a milder sweetness.
Swap digestive biscuits for chocolate-flavoured biscuits or graham crackers for a different base flavour.
Add a layer of chopped nuts or caramel between the biscuit base and mousse for extra texture.
Top with fresh raspberries, mint leaves, or orange zest to add a fruity or zesty twist.
Use flavored extracts (like almond or orange) instead of vanilla for a subtle variation.

Storage/Reheating

Store the dessert in the fridge, covered, and it will keep for up to 2 days. It’s best served chilled — do not attempt to reheat, as the mousse texture will be compromised. If preparing ahead, assemble and chill overnight.

FAQs

What size of tin should I use?

Use a deep 20 cm (8 inch) square cake tin, lined with foil to allow easy removal.

Can I use a different type of biscuit for the base?

Yes — you can substitute digestive biscuits with chocolate biscuits, graham crackers, or any other lightly sweetened biscuit you prefer.

Do I need to use gelatin?

Yes — the gelatin helps the mousse set firmly enough to cut into squares and hold its structure over the biscuit base.

Can I make this without raw egg whites/yolks?

This recipe uses raw eggs. If you prefer to avoid raw eggs, you may need to use a mousse recipe designed for egg-free preparation, or use pasteurised eggs and still proceed carefully.

Can I prepare this the day before?

Yes — in fact, preparing it the day before and chilling overnight will enhance the set and make slicing cleaner.

How do I serve it nicely?

Cut into neat squares, serve chilled. You can garnish with a dollop of whipped cream, a dusting of cocoa powder, or fine shavings of chocolate on top.

Can I freeze leftovers?

Freezing is not recommended, as the texture of the mousse may change and become less creamy upon thawing.

What if the mousse mixture becomes too thick before folding in whipped cream?

If it thickens too much, you can gently warm it very slightly (off heat) to loosen it, but be careful not to overheat. Then allow it to cool again before folding in the cream.

Why should I not let the milk mixture boil?

Boiling can curdle the egg yolks and affect the smooth texture of the mousse. Gentle thickening ensures a silky finish.

How can I make this gluten-free?

Use gluten-free biscuits for the base, and ensure all other ingredients (including chocolate chips and gelatin sachets) are certified gluten-free.

Conclusion

This dessert brings together a crunchy biscuit base and luxuriously smooth chocolate mousse for a treat that looks impressive yet is straightforward to make. With a little planning to allow the mousse to set, you’re rewarded with a refined ending to any meal — and plenty of room for creative variations.