Preheat the oven to 350°F. Line a 9-inch round cake pan with parchment paper. Whisk eggs and sugar until tripled in volume. Sift and fold in flour, cocoa powder, baking powder, and salt gently. Bake for 13-14 minutes.
Boil water and sugar until dissolved. Let cool.
Make ganache with hot cream and chocolate, then add bloomed gelatin. Fold in whipped cream in portions.
Prepare ganache with white chocolate, cream, and coffee. Add bloomed gelatin and fold in whipped cream.
Brush simple syrup on sponge. Use acetate to layer chocolate mousse, then mocha mousse. Refrigerate overnight.
Pour ganache glaze over the cake and let it drip down. Smoothen and serve chilled.