Beat the butter until frothy, pour in the sugar and stir.
Stir in the eggs one at a time.
Mix the flour, baking powder and add to the dough.
Add lemon zest, rum and salt and stir well.
Place the dough in a greased springform pan (26 cm diameter).
Peel and quarter the apples. Score and distribute evenly on the dough.
Scatter the almonds on top and bake for 60 minutes at 180 ° C in a preheated oven.
After baking, brush the apples with jam (possibly quince jelly or apricot jam) so that they don't dry out too much.
Sprinkle with powdered sugar before serving.