The cake:
1. Peel and cut the apple into small cubes. Melt the knob of butter in a skillet over medium heat and fry the diced apple for 2-3 minutes, add the tablespoon of sugar, lower the fire and continue cooking for 2 minutes. Allow to cool.
2. In a bowl, beat butter with the remaining sugar with a whisk. When the mixture whitens, add egg and milk.
3. Mix the flour and baking powder and add to the mixture. Stir in the diced apple.
4. Line you muffin or cupcake pan with individual paper cups. Divide batter to fill the cavities. Bake in a preheated oven for 15 minutes at 390°F (200°C).
5. Remove from oven and put the cupcakes on a cooling rack.
The topping:
1. Whisk the Biscoff spread with a little mascarpone, then gently fold in all the mascarpone
2. Fill a pastry bag with the frosting.
3. Once the cupcakes are completely cooled, decorate with the frosting and chill until serving.
