For the caramel, heat 200 g sugar and 50 ml water until the sugar has melted and taken on a nice caramel colour.
Take the pot off the stove. Add 125 g butter and mascarpone, season with 1 pinch of salt. Bring to the boil briefly until the caramel has dissolved.
Cream 175 g butter, 200 g sugar and 1 pinch of salt with the whisk of the hand mixer. Stir in the eggs one after the other. Mix flour and baking powder, stir in briefly. Stir in 200 g oat flakes.
Put approx. 2/3 of the dough into a greased rectangular springform pan (24 x 36 cm) and press until smooth. Spread chocolate droplets and caramel on top one after the other. Knead the rest of the dough and 50 g oat flakes and crumble over them as a crumble.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 12 minutes. Remove from the oven, leave to rest in the mould for approx. 10 minutes, remove from the mould and allow to cool.
Cut into pieces.