Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Plums, wash, halve and stone. Grease square springform pan (24 x 24 cm; alternatively round, 26 cm Ø).
Break chocolate into pieces. Melt with 250 g butter in a pot while stirring at low heat.
Separate two eggs. Beat egg whites until stiff. Whisk the remaining eggs, egg yolk and sugar with the whisk of the mixer for about 4 minutes until creamy. Stir in hot chocolate butter bit by bit. Stir the flour briefly into the chocolate egg mixture.
Fold in 2 portions of beaten egg white. Smooth in the mould. Spread plums on top. Bake in a hot oven for 30-35 minutes. (Stick test! In the brownie stick test, you should still see soft traces of dough on the wooden skewer.
Only then is the brownie nice and juicy after cooling down. Angie prefers to bake it the day before and keep it covered and cold overnight - afterwards it can be cut perfectly and tastes almost like a chocolate filling.
If you prefer classic chocolate cake, leave the brownie in the oven for about 10 minutes longer :-).
Take out the cake, let it cool down and cover and put it in a cool place.