Preheat the oven for 160°C.
Whisk butter, sugar, cinnamon, egg, crème fraiche, flour and baking powder together to make a fluffly dough. Fill into muffin moulds (butter and flour them before!).
For the crumble, mix flour with brown sugar, cinnamon and the melted butter. Place the apple slices on top of the tarts and cover with cinnamon crumble.
Bake for 30 minutes and serve with ice cream.