Melt the butter and let it cool. Whisk egg and sugar until white and puffy. Add flour, baking powder, milk and butter.
Pour the batter into an oven tray covered with grease proof paper. Bake for 20-25 minutes in 175°C.
Mix all ingredients for the topping in a saucepan. Heat it up and stir well. Spread the topping over the almost ready cake and bake for 10 more minutes.
A real tosca has a topping made by almond, cream and butter. Tosca was the name of an opera by Puccini in the early 1900’s. The cakes has probably got it’s name from the opera (don’t ask me why).