Wash the plums, cut them in half, stone them and cut the halves into thin slices. Line a square baking tin (approx. 24 x 24 cm) crosswise with 2 wide strips of baking paper.
Melt butter and peanut cream in a pot. Stir in sugar, honey and oatmeal. Put about half of the mixture into the mould, smooth it down. Spread plums on it, spread the remaining oat flakes over it.
Press firmly and bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 25 minutes until golden brown. If the surface becomes too dark, cover with foil.
Remove from the oven and let it cool down lukewarm on a cake rack. Then chill for about 3 hours. Lift the oatmeal plate out of the tin with the help of the baking paper. Carefully cut the plate into about 25 pieces.
Keep muesli bars cold until serving.