Cover the bottom of a springform pan (26 cm Ø) with baking paper. Separate the eggs. Beat the egg white with the whisk of the hand mixer until stiff. Add 125 g sugar and salt. Stir in the egg yolks one by one. Mix flour and baking powder, sieve onto the egg cream and fold in carefully. Fill the mixture into the springform pan and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 20-25 minutes. Remove from the oven and let it cool down in the mould on a cake rack.
Wash, clean and halve the strawberries. Puree about 250 g finely. Remove the bottom from the mould. Peel off baking paper. Cut the cake 2x horizontally. Place a cake ring around the lower cake base. Soak gelatine in cold water. Mix mascarpone and 75 g sugar until smooth. Stir in strawberry puree. Squeeze out the gelatine and dissolve it carefully in a small pot at low heat. Stir in 2-3 tablespoons of cream, then stir into the remaining cream. Whip 300 g cream until stiff and fold in. Pour a good 1/3 of the cream onto the base in a ring and smooth it down. Spread 350 g strawberries on the cream. Place the middle cake base on top. Add about 1/2 of the remaining cream and smooth it down. Place the upper cake layer on top. First spread the rest of the cream, then the remaining strawberries. Chill for about 2 hours.
Mix the casting powder in a small pot with 3 tablespoons of sugar. Gradually stir in 250 ml of cold water with a wooden spoon. Heat while stirring, bring to the boil briefly. Spread it quickly on the strawberries with a tablespoon. Chill the cake for about 1 hour.
Stir icing sugar with milk until smooth and colour pink with food colouring. Pour the icing into a small freezer bag, cut off a small corner. Decorate the waffle hearts with the icing, let them dry. Beat 150 g cream until stiff. Remove cake ring. Spread the edge of the cake with the cream until smooth. Place the waffle hearts on top.