Ingredients
Pan sizes, times and temperatures in the method are not scaled.
Cocoa sheets
Vanilla sponge
Vanilla pudding cream
Jam and glaze
Method
Cocoa sheets
Heat the oven to 350°F (180°C). Dissolve the baker's ammonia (1 tsp) in the vinegar (5 g1 tsp). Mix the eggs (2), granulated sugar (100 g½ cup), sunflower oil (80 ml⅓ cup), milk (50 ml3½ tbsp) and the dissolved leavening. Add the cocoa powder (30 g6 tbsp) and all-purpose flour (300 g2½ cups) to form a soft dough.
Divide in 2. Roll each onto the back of a greased and floured 25 × 35 cm (10 × 14 inch) pan and prick with a fork. Bake each 13 to 15 minutes.
Sponge
Beat the eggs (4) with the granulated sugar (120 g½ cup + 2 tbsp) until very voluminous. Fold in the all-purpose flour (120 g1 cup) and salt.
Pour into a lined pan of the same size and bake at 350°F (180°C) for 20 to 25 minutes. Cool.
Cream
Heat the milk (750 ml3¼ cups). Whisk the egg yolks (3), granulated sugar (120 g½ cup + 2 tbsp) and flour or cornstarch (60 g½ cup + 1 tbsp), whisk in some of the hot milk, then pour it all back into the pot. Cook, whisking, until thick. Add the vanilla (1 tsp) and cool completely.
Beat the butter (200 g¾ cup + 2 tbsp) until fluffy and fold in the cooled pudding.
Assembly
Lay one cocoa sheet in the pan and spread half the cream over it. Spread both sides of the sponge with the apricot or strawberry jam (150 g) and lay it on top. Spread the rest of the cream and top with the second cocoa sheet.
Wrap in plastic and press under a weight overnight.
Glaze. Melt the dark chocolate (100 g) with the butter (30 g2 tbsp) and sunflower oil (14 g1 tbsp). Spread it over the top and let it set. Cut into rectangles.