The day before for 2 biscuits, line two baking trays (each approx. 35 x 40 cm) with baking paper. Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Separate 4 eggs per biscuit. Beat the egg whites and 4 tablespoons of cold water with the whisks of the mixer until stiff. Finally, add 125 g sugar and 1 pinch of salt.
Stir in the egg yolks one after the other. Stir in 1 bag of jelly powder and approx. 1 teaspoon of food colouring. Mix 75 g flour, 75 g starch and 1 teaspoon baking powder, sieve onto the egg foam and carefully fold in.
Spread the sponge mixture on a baking tray. Bake in a hot oven for 10-12 minutes. Sprinkle a clean tea towel with about 2 tablespoons of sugar. Loosen the edge of the sponge cake and turn it over onto the tea towel. Carefully remove the paper immediately.
Let the sponge cool down. Bake another 1 sponge cake and let it cool down.
For the filling, stir mascarpone, milk, sugar and vanilla sugar until smooth. Whip cream until stiff and fold in. Cut a total of 6 squares from both biscuits (3 pieces of approx. 19 cm edge length; 3 pieces of approx. 12 cm edge length).
Use the rest of the sponge cake for other purposes (e.g. cut out hearts and use them as decoration of the cake buffet). Spread the cream on 2 sponge squares of the same size each, approx. 1 1⁄2 cm thick and place on top of each other.
Cover each with the third sponge cake of the same size. Press on lightly. Smooth both layer cakes all around. Chill for about 30 minutes.
Whisk butter and 200 g icing sugar with the whisk of the mixer for approx. 15 minutes until creamy. Spread both cakes with this mixture all around and chill overnight.
The next day, sieve 300 g icing sugar for the fondant. Melt the marshmallows with 3 tbsp. water in a microwaveable container at 600 watts for approx. 2 1⁄2 minutes. First gradually stir in the icing sugar with a wooden spoon, then knead with your hands to form a smooth, supple fondant mass.
Roll out approx. 2⁄3 on a little icing sugar to a square plate (approx. 42 x 42 cm) approx. 2 mm thin. Cover the larger cake with it, pressing it all around. Cut off any excess fondant.
Knead with the rest of the fondant. Also roll out to a 2 mm thin square (approx. 30 x 30 cm). Cover the smaller cake with it. Press on all around. Cut off any excess fondant. Roll 2 thin strands (each approx. 1⁄2 cm Ø) from the rest of the fondant and twist into a cord.
Place the small cake in the middle of the large cake. Decorate with the cord.