Wash, stalk and stone the cherries. Select raspberries and blackberries, wash if necessary. Stir jam until smooth. Carefully mix in the fruit.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease square springform pan (24 x 24 cm; alternatively round, 26 cm Ø). Break chocolate into pieces for the dough.
Melt with 250 g butter in pieces in a saucepan at low heat.
Beat the eggs, sugar and 1 pinch of salt with the whisks of the mixer for 3-4 minutes until creamy. Remove the chocolate butter from the heat and immediately stir into the egg mixture.
Mix flour, cocoa and baking powder. Quickly stir into the chocolate-egg mixture.
Put the dough into the mould and smooth it down. Spread fruit on top. Bake in a hot oven for about 30 minutes. Take out and let cool down. Remove from the form. Cut into pieces of about 4 x 4 cm.