Preheat the oven to 355 degrees F (180 degrees C). Grease a loaf pan.
Combine butter, sugar, and vanilla sugar in a bowl and beat with an electric mixer until creamy. Add eggs, 1 at a time, beating well after each addition. Mix in rum.
Sift flour, cornstarch, baking powder, and salt into a separate bowl; stir into butter mixture, 1 tablespoon at a time. Mix in almond flour and chocolate sprinkles. Pour cake batter into prepared loaf pan.
Bake in the preheated oven until a toothpick comes out clean, about 1 hour. Turn off oven and leave cake in the warm oven for 10 more minutes.
Remove from oven and carefully unmold onto a wire rack. Cool completely before serving.