I made this cake over the course of two days as I didn’t have a clear run at it (lots of unexpected interruptions), but it was no worse the wear for it. The filling (and coating) is a chocolate-flavoured crème mousseline which may look complicated but is, in fact, just a pastry cream whipped with melted chocolate and softened butter. The candied walnuts are delicious: the danger is, if you make them the day before, there may not be any left to decorate-such is their moreishness. The cake will serve at least 10 so is perfect if you have a houseful or you are celebrating a special occasion.
- For the mocha meringue
- 190g egg whites (about 5 large)
- 380g caster sugar
- 4 teaspoons espresso powder
- ¼ teaspoon cream of tartar
- For the chocolate mousseline
- 130g plain chocolate (70% cocoa solids) broken up
- 400ml whole milk
- 3 large egg yolks
- 100g caster sugar
- 30g cornflour
- 200g unsalted butter, softened at room temperature
- For the candied walnuts
- 90g walnuts
- 2 tablespoons caster sugar
- Heat the oven to 140˚c, fan oven 120˚c, mark ¼. Line 2 flat baking sheets with non-stick baking parchment. Draw two, 22cm diameter circles on each sheet. Place the egg whites in a clean mixing bowl and whisk to stiff peaks. Mix the caster sugar with the espresso powder and whisk into the egg whites a tablespoon at a time until very stiff and glossy. Whisk in the cream of tartar. Continue whisking until the meringue mixture doesn’t feel grainy when rubbed between your fingers.
- Divide the meringue between the two circles and spread to the edges. Cook in the oven for 2 hours. Turn the oven off and leave the meringues for a further 2 hours. Remove from the oven and carefully peel the meringue discs off the paper. Store in an airtight container if you are not completing the cake that day.
- For the chocolate mousseline, melt the chocolate in 30 second bursts in the microwave or put the chocolate in a bowl sitting over a saucepan of barely simmering water. Stir until melted and set aside.
- Pour the milk into a saucepan and bring to just below boiling point. Meanwhile, in a mixing bowl beat together the egg yolks, sugar and cornflour. Pour the scalded milk over the egg yolks and stir. Clean the saucepan (the milk can catch at the bottom) and pour the liquid back into the saucepan. Stir over a low heat until the mixture thickens. Cook for 1 minute then take off the heat. Beat in the melted chocolate. Cover the surface with a sheet of cling film to prevent a crust forming and chill.
- When the pastry cream is cold scrape into a mixing bowl. Gradually beat in the softened butter. Chill until ready to assemble the cake.
- For the candied walnuts, heat the oven to 200˚c, fan oven 180˚c, mark 6. Toss the walnuts in 1 tablespoon of water. Lay the nuts on a baking tray lined with non-stick parchment paper and sprinkle over the sugar. Cook for 10-12 minutes, until the nuts are golden and sugar has almost caramelised. Remove and leave to cool.
- To assemble the cake, place a meringue disc, flat side down, on a serving plate. Spread about a third of the chocolate mousseline on top and spread to the edges. Place the second meringue disc on top, flat side down, and cover the top and edges with the remaining mousseline icing. Reserve about 8-10 of the whole walnuts and finely chop the rest. Arrange the whole walnuts around the edges and sprinkle the rest over the top.