Separate the egg. Beat the egg whites with 1/3 of the sugar until stiff. Beat the butter until fluffy. Beat the egg yolks with the remaining sugar, vanilla sugar, lemon zest, lemon juice, and stir into a creamy mixture. Stir in the almonds with the flour and baking powder. Fold in the egg whites.
Line the bottom of a springform pan with parchment paper. Transfer the batter into the springform pan. Bake in the preheated oven at 200°C (approximately 400°F) for about 1 hour. If the cake gets too dark, cover with aluminum foil. Soak the hot cake with the almond liqueur. Sprinkle the cake with powdered sugar.