Peel the 4 large apples and cut them into eighths. Arrange them in a greased springform pan or baking dish, overlapping like roof tiles. Drizzle with lemon juice and a splash of rum or calvados.
In a bowl, beat 75 g butter for 2 minutes until creamy. Add 125 g powdered sugar and mix well. Stir in 150 g grated almonds until well combined.
Spread the almond mixture evenly over the apples. Bake in a preheated oven at 180°C (356°F) for 15 minutes.
Serve warm with vanilla ice cream or ice-cold whipped cream.