Mix the butter, peanut butter and sugar until creamy. Stir in the eggs one at a time. Mix flour, baking powder, sieve and mix in 3 parts. If the dough is too dry, stir in 3 - 6 tablespoons of milk.
Put the dough in a greased dish (20 cm) and bake in the oven preheated to 175 ° C for 50 - 60 minutes.
Bring all the ingredients for the topping to the boil over a medium heat for about 1 minute while stirring. Spread the icing on the cake.