For the apple mousse cake, quickly knead all the ingredients for the dough together and chill for half an hour.
Peel five apples, remove the core, cut into small pieces and mix with the cinnamon.
Grease and flour a small springform pan (Ø 20 cm).
Press two thirds of the dough into the form, pull up the edges a little.
Spread the cinnamon apples on top and cover with the remaining third of the dough.
Bake in the oven at medium heat (180 °C) for about 40 minutes.
In the meantime, peel and chop the remaining apple. Steam in a small saucepan with a little water and the juice of the lemon until the apple pieces break down. Sweeten to taste.
Beat the whites of the 3 eggs until stiff peaks form, whip again with the powdered sugar and gently fold in the apple puree and orange liqueur by the spoonful.
Once the apple pie has browned slightly in the oven, spread the apple whipped cream on top and bake for another 5 minutes.
Serve the apple mousse cake with semi-stiff whipped cream.