For the apple tart, cream the sugar with the eggs. Mix the flour and baking powder and then sift into the eggs. Mix everything together well and season with the lemon zest and rum.
Peel, core and slice the apples and mix into the batter. Grease a springform pan with margarine, pour in the batter, smooth it out and bake in a preheated oven at 180 °C for about 70 minutes.
Sprinkle the cooled cake with sugar.