Wash the plums, drain, stone and quarter them. Melt 75 g butter in a saucepan, add 50 g sugar and dissolve, do not brown. Add cream and bring to the boil. Stir in oat flakes and let cool down.
In the meantime, warm up the milk. Slowly melt 50 g sugar over medium heat until it turns light brown. Add milk while stirring and bring to the boil once. Mix 2 eggs, egg yolk, 50 g sugar and vanilla pulp.
Add to the caramel milk and stir at low heat until a slightly thick-creamy consistency is obtained. Do not let it boil! Remove from the stove. Beat the fat with the whisk of the hand mixer until foamy.
Gradually add the remaining sugar and the eggs and stir until creamy. Mix flour and baking powder and stir in together with the caramel cream. Fold in the walnuts. Grease a springform pan (26 cm Ø), sprinkle with breadcrumbs, fill in the dough and spread evenly.
Place the plums close together on the dough surface. Spread the oatmeal mixture evenly on the plums. Bake in the preheated oven (electric range: 175-200 ° C/ gas: level 2-3) for 60-70 minutes.
Leave to rest for 10 minutes in the open oven. Makes about 16 pieces.