Sponge:

• Using a mixer, combine the room-temperature butter and sugar, mixing until it becomes a fluffy white cream. Separately, combine the flour with the cocoa powder, walnuts, salt, baking powder, and baking soda.
• Add the eggs to the buttercream, one at a time, alternating with a spoonful of dry ingredients – so, one egg, then one spoonful of dry ingredients – mixing well each time. When the three eggs are combined, add half of the remaining dry ingredients and the yogurt (at room temperature). Mix slowly until smooth. Continue with the remaining dry ingredients and the hot coffee. Don't over-mix, just make sure the mixture is uniform.
• Preheat the oven to 180°C (360 °F). Line a large 30/40 cm (12x16 inches) baking tray with parchment paper. Pour the mixture into the tray and level it nicely with a spoon. Bake for 20-25 minutes, until the edges pull away from the tray. When it is ready, flip it onto a cooling rack and cut it into two 20/30 cm (10x14 inches) pieces.
• Wash the cherries, remove the pits, and leave them to drain.

Chocolate Cream:

• Place the milk over a low heat. Separately, whisk the eggs with a pinch of salt. Add the sugar and starch and continue to whisk until the mixture is smooth.
• Incorporate a few tablespoons of the hot milk into the egg cream. Pour the egg cream over the milk and keep the mixture on medium heat. Stir continuously until it thickens and starts to boil. Turn off the heat and add the vanilla.
• Divide the mixture into two parts, one-third, and two-thirds. Into two-thirds of the cream, add the dark chocolate broken into pieces and 100 g (3 3/4 oz) butter. Over one-third of the cream, add the milk chocolate pieces and 50 g (1.5 oz) butter. Leave the cream to rest for 2-3 minutes, then vigorously stir the creams until they achieve a smooth consistency.
• Cover with cling film and refrigerate for 2-3 hours.

Assembly:

• Place half the cake on a baking tray. Pour half on the dark chocolate cream and place the cherries on top. Pour the rest of the dark chocolate cream over the cherries. Cover with the other half of the cake. Spread the milk chocolate cream on top.
• Refrigerate until the next day.
• Before serving, dust the cake with dark cocoa powder and decorate it with chocolate and cherries. Before cutting, run the knife blade under hot water. It is a wonderful cake, full of flavors and chocolate. Everyone who tastes it will be delighted.

Enjoy!