Chocolate Mousse Cake

Ingredients

• 1/2 cup packed light brown sugar ((100g / 3 1/2oz))
• 1/4 cup caster sugar (superfine sugar) ((50g/1.8oz))
• 1/2 cup buttermilk ((125ml))
• 1 teaspoon instant coffee granules
• 1/4 cup neutral flavoured vegetable oil
• 1 large egg
• 1 teaspoon vanilla extract
• 130 g plain flour (all-purp flour) ((1 cup spooned & levelled / 4.6oz))
• 30 g Dutch-processed cocoa powder ((1/4 cup / ~1oz))
• 1 teaspoon baking powder
• 1/4 teaspoon salt
• 2 1/2 cups whipping cream (divided 3/4 cup:1 3/4cup (625ml))
• 200 g dark chocolate (semisweet chocolate/50% cocoa solids) ((7oz))
• 57 g unsalted butter ((1/2 stick / 1/4 cup))
• 2 tablespoons icing sugar ((25g/~1oz) (notes 1))
• 1/2 cup water ((125ml))
• 2 teaspoons powdered gelatine
• 1/2 cup whipping cream ((125ml))
• 3/4 cup caster sugar (superfine sugar) ((150g / 5.3oz))
• 55 g Dutch processed cocoa powder ((1/2 cup spooned & levelled/2oz))

Instructions

1. 1

   FOR THE CAKE: Grease and line an 8 inch / 20cm round springform tin with baking paper. Preheat the oven to 180C (160C fan forced) / 350F.

2. 2

   In a large bowl, dissolve the coffee granules into 2 tablespoon of hot water. Add the buttermilk, sugars, oil, egg and vanilla until well combined.

3. 3

   Sift over the flour, cocoa, baking powder and salt then stir with a rubber spatula until just combined.

4. 4

   Pour the batter into the prepared tin and bake for around 20-22 minutes, until a toothpick inserted comes out with just a crumb or two attached.

5. 5

   Immediately, use a flat bottomed glass to gently press all over especially pressing out towards the sides to get a flat cake top (the other option is the cut the dome once it’s cool off but doing it this way means you don’t waste cake and you get a fudgier texture at the end).

6. 6

   Run a knife around the edge of the cake to make sure it isn’t sticking to the sides of the pan.- If you aren’t going to use the acetate to form your mousse, just leave the cake in the pan as it is, to cool.- If you are going to use acetate to form your mousse, then lift out the baking paper sides and unspring the cake pan sides to help it cool quicker.

7. 7

   You can place it into the fridge or freezer to speed things up too.

8. 8

   FOR THE CHOCOLATE MOUSSE (only once the cake has cooled): Place the finely chopped chocolate, cubed butter and sugar into a medium bowl.

9. 9

   Heat ¾ cup (180ml) of the cream in a small saucepan just until it’s heavily steaming and close to starting to simmer. Pour it immediately over the chocolate and butter, then let it sit for a minute before stirring to a smooth ganache. If it’s not melting together smoothly, just zap it in the microwave for 20 seconds and stir again (or sit the bowl over a pan of simmering water, without it touching the water).

10. 10

    Let the ganache cool to room temperature before proceeding. You can speed it up in the fridge if you like.

11. 11

    In a large bowl with a balloon whisk or electric beater, beat the remaining 1 ¾ cups cream to soft peaks.

12. 12

    Using a spatula, stir about ½ cup of the whipped cream straight through the ganache to lighten it. Now fold the remaining cream, in two parts, into the mousse until just mixed through. Be very careful not to overmix the mousse or you'll knock the air out, making it dense.

13. 13

    If using acetate to form the mousse (if not skip to the next step), reset the side of the cake pan around the cake and slot the acetate down around it, making sure it’s pressed down past the sides of the cake. Stick it where it joins with sticky tape.

14. 14

    Spread the mousse over the cake base, then smooth out the top with an offset spatula as smooth as possible. Chill 3 hours or overnight is even better.

15. 15

    FOR THE CHOCOLATE MIRROR GLAZE (this can take up to an hour to cool to the right consistency so you can start it towards the end of the mousse cake chilling time).Sprinkle the gelatine over ¼ cup (60ml) of the water and allow it to ‘bloom’ for 5 minutes while you get on with the rest.

16. 16

    Combine the other ¼ cup of water, the cream, sugar and cocoa in a saucepan over low heat. Whisk to combine then use a spatula to stir over low heat, until the sugar has dissolved completely. Keep the heat low, it must not come to a boil.

17. 17

    Add the gelatine and water mixture and whisk in thoroughly. Again, it must not boil.

18. 18

    Pour the glaze through a sieve into a jug (to remove any lumps). Now place the jug in the fridge or even the freezer until it cools enough to coat the back of a metal spoon thickly. You want to be slightly above room temperature but not too warm or it will melt your mousse as soon as you pour it on. Too cold and it will begin to set before it covers the cake. If there is a light film or skin on the top of the glaze, make sure to skim that off with a spoon before using.

19. 19

    Remove the outer frame of the spring form tin and the baking paper or acetate carefully. Optional extra step: If you want to smooth the mousse out a little around the sides and top see the notes section.

20. 20

    With the cake still on the baking tin base, sit it on top of a wire rack over a baking tray with sides. Pour all of the glaze over the cake and around the edges so it falls down the sides, quickly and confidently. Use a large flat metal spatula to smooth it over a little, being careful not to press into the mousse. Lift the wire rack and set it aside, then use a silicone spatula to scrape all the excess glaze back into your jug to pour over a second time. Move quickly so that your glaze doesn’t set too quickly on the cake.

21. 21

    Leave the cake in the fridge to set for at least an hour before carefully removing the base. The tin base should come away fairly easily, then holding the cake underneath with one hand, use the other to peel back the baking paper halfway. Swap hands and remove the paper entirely. Use a sharp knife to run around the bottom edge to tidy up where the set glaze is not straight. Transfer to a cake plate and serve. Use a sharp, warmed knife to cut nice smooth slices.

22. 22

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