Name: How to make a chocolate mousse cake
Prep time: 30 min
Cook time: 25 min
Total time: 55 min
Yield: 10
Ingredients: Chocolate sponge; 4 egg yolks; 170 gm pure icing sugar, sieved; 185 gm eggwhites (about 6); 65 gm Dutch-process cocoa powder; 20 gm cornflour; Soaking syrup; 25 gm caster sugar; 1½ tsp Grand Marnier, or liqueur of choice; Chocolate truffle mousse; 325 gm dark chocolate buttons (53% cocoa solids); 68 gm liquid glucose; 68 gm caster sugar; 475 gm pouring cream; Chocolate icing; 150 gm dark chocolate buttons (53% solids); 60 gm pouring cream; Caster sugar, for dusting; Chocolate curls, to serve

Prepare to be happy. This layered chocolate mousse cake has a lovely texture and rich chocolate flavour, yet is simple to make. The beauty of it is that it can also be made ahead and frozen in preparation for a special occasion.

The cake base

For the cake base, I like to use a roulade sponge – it has no fat content so it can be refrigerated without becoming hard, and it has a lovely light texture that balances well with mousse. Whisk the yolks and some of the sugar in an electric mixer on medium speed, being careful not to overwhisk or the sponge will be dense; this goes for whisking the eggwhites, too – just whisk them till they hold stiff peaks. When folding the eggwhites into the yolks, and then the cocoa-cornflour mixture, fold the mixture just until everything is incorporated to reduce the loss of aeration. And sieve your cocoa and cornflour first to avoid any lumps.

To give the cake base a richer flavour, brush it liberally with a simple light sugar syrup with an added liqueur of your choice; I like Grand Marnier, a classic pairing with chocolate. Do the brushing when both the syrup and sponge are cool. The syrup not only introduces another flavour, but it also helps to prevent the sponge drawing moisture out of the mousse, which would cause it to dry out and shrink.

The mousse

Next comes the mousse. There are many ways to make chocolate mousse, but this method is my favourite – the secret is to use whipped cream, which aerates the mixture, resulting in a beautiful texture that melts in your mouth, while the flavour is nicely rounded and not too sweet. The important factors are the fat, or cream, and the type of chocolate, of course. You cannot interchange the chocolate in this recipe – there is a fine balance of liquid to chocolate. If you use a chocolate with a percentage higher or lower than 53 per cent cocoa solids the mousse won’t have the best texture. With a lower content it will not set properly, and as you go higher the mousse will become firmer and eventually split and have a terrible texture.

When you’re mixing the mousse it’s most important to form a good emulsion when you add the syrup and the initial quantity of cream to the chocolate; otherwise it won’t set properly. Once the syrup has been incorporated you should have a smooth, shiny, slightly elastic emulsion; before adding the cream, whip it to just before soft peaks form.

An emulsion is the combining of two ingredients that don’t normally combine, fat and liquid. This is key to achieving a smooth, creamy texture, and it enhances the true taste of the chocolate. If the emulsion is not achieved, the mix becomes unstable and when the remaining whisked cream is folded into the chocolate, the two don’t combine properly. If you’re mixing by hand, mix energetically with small circular movements in the centre of the mixture to ensure the fat and water become homogenous, which stabilises the mixture; visually it will be elastic and shiny. Generally, if you’re using a stick blender it will emulsify well.

The icing

The icing is straightforward; use it when it has cooled but is still fluid. Once the mousse has set in the fridge for at least six hours, pour the icing on top while it’s in the ring and tilt it to cover the entire surface. At this point the cake can be frozen (for up to a month); defrost it in the fridge when you’re ready to serve it.

Once the icing has set, remove the ring. If you’re using a deep metal ring or springform tin, gently heat the outside with a blowtorch until it easily slips off the cake; or run a hot knife around the inside of the ring, then refrigerate the cake again to firm it up. If you’re using acetate sheets, as we have here, just peel them away from the cake; no heat is required. Acetate sheets are great for creating a higher mould; just cut them to your desired height and line the inside of the mould.

We’ve decorated the cake with chocolate curls; you could also use roasted nuts, praline or berries. Or coat the cake completely in chocolate. Spray a fine mist of canola spray onto a bench and put a piece of plastic wrap large enough to cover the cake on top, smoothing it out to remove all the creases. Pour melted chocolate in the centre, then spread it with a palette knife into a disc large enough to cover the top and sides of the cake. The chocolate only needs to be 2mm-3mm thick. Have the cake close to you then pick up the plastic wrap by the corners furthest away and place it chocolate-side down on the cake, ensuring it hangs down to cover the sides. Smooth down the sides and run a small knife around the base of the cake to form a neat edge. Refrigerate it for at least 10 minutes or until you’re ready to serve, then simply peel off the plastic wrap and decorate it.

To serve, use a warm knife to cut the cake and don’t leave it sitting at room temperature for long, or it will soften. I serve it with crème Chantilly (whipped cream sweetened with icing sugar and vanilla) – it’s billowy and perfect with the lush mousse.

Ingredients

Chocolate sponge

4 egg yolks

170 gm pure icing sugar, sieved

185 gm eggwhites (about 6)

65 gm Dutch-process cocoa powder

20 gm cornflour

Soaking syrup

25 gm caster sugar

1½ tsp Grand Marnier, or liqueur of choice

Chocolate truffle mousse

325 gm dark chocolate buttons (53% cocoa solids)

68 gm liquid glucose

68 gm caster sugar

475 gm pouring cream

Chocolate icing

150 gm dark chocolate buttons (53% solids)

60 gm pouring cream

Caster sugar, for dusting

Chocolate curls, to serve

Method

1.For sponge, preheat oven to 190C. Line an oven tray with buttered baking paper and dust with caster sugar. Whisk yolks and 160gm icing sugar in an electric mixer on medium-high speed until thick and a ribbon holds (4-5 minutes). Be careful not to overwhisk the mixture.

2.Whisk eggwhites in a separate bowl with remaining sugar just until stiff peaks form.

3.Fold a third of the eggwhite into yolks, then fold in remaining. Just before eggwhites are completely incorporated, sieve cocoa and cornflour over and fold to just combine.

4.Gently spread batter onto prepared tray to a 22cm-diameter round with a palette knife (mixture will continue to spread a little; which is fine), then bake until cake springs back when gently pressed (12-18 minutes). Set aside to cool completely (25-30 minutes).

5.Trim cake to fit into a 22cm-diameter ring mould or the ring of a springform tin, using the mould as a guide. Place ring on a tray lined with baking paper, then line ring with strips of acetate sheet to increase the height (see note). Place cake base inside and set aside.

6.For soaking syrup, bring sugar and 50gm water to the boil in a small saucepan over medium heat, stirring to dissolve sugar. Allow to cool, then add liqueur and brush liberally over sponge.

7.For mousse, place chocolate in a heatproof bowl and have a spatula on hand. Stir glucose, sugar and 68gm water in a small saucepan over low heat to dissolve sugar, then increase heat to high and bring to the boil. Remove from heat, pour directly onto chocolate and stand for a minute, then mix vigorously from the centre with a spatula until chocolate becomes smooth, glossy, elastic and reaches 35C on a sugar thermometer.

8.Whisk cream just until soft peaks form, add a quarter to chocolate mixture and mix vigorously from the centre to combine, then fold in remaining cream in small additions.

9.Pour chocolate mousse into ring over cake and refrigerate covered until set (6 hours or overnight)

10.For icing, melt chocolate in a heatproof bowl over a pan of simmering water. Bring cream and 60gm water to the boil in a saucepan over medium-high heat, pour onto chocolate and stir until smooth. Cool, then pour onto cake in the ring and refrigerate to set (30 minutes to 1 hour). Remove ring and acetate sheets, and serve cake chilled topped with chocolate curls.