Grease and line a 33x23cm Swiss roll tin with parchment and a silicone sheet.
Cream butter and icing sugar, beat in egg whites, then fold in flour and cocoa.
Spread paste on the silicone mat, create a pinstripe pattern with a comb, and freeze for 15 minutes.
Preheat the oven to 220°C.
Whisk egg whites with caster sugar to create a glossy meringue.
Whisk almonds, icing sugar, and whole eggs for 5 minutes before folding in flour, meringue, and melted butter.
Place the frozen decorative paste into the lined tin.
Spread the joconde mixture over the paste and bake for 5-7 minutes.
Turn the cake onto parchment, peel off the mat, and cool.
Line 6 chefs' rings with parchment and create a 17x5cm paper template.
Cut sponge strips using the template and press them into the rings with the stripes facing out.
Cut 4cm circles from cake trimmings and place them in the base of the rings.
Melt dark chocolate over a pan of simmering water.
Stir in butter, egg yolks, and brandy.
Whisk egg whites to stiff peaks and fold into the dark chocolate.
Whip cream to soft peaks and fold into the dark chocolate mixture.
Pipe dark mousse into the rings until three-quarters full and freeze briefly.
Gently melt the white chocolate over simmering water.
Whisk an egg white to stiff peaks and fold into the white chocolate.
Whip cream to soft peaks and fold into the white chocolate mixture.
Pipe white mousse to the top of the rings and chill in the fridge until set.
Remove from rings, top with berries, and dust with icing sugar.