Chopping chocolate. Melt butter and chocolate over a warm water bath. Mix flour and baking powder. Mix 180 g sugar, salt, vanilla sugar and eggs with the whisk of the hand mixer until slightly creamy.
First stir in the chocolate butter and then the flour mixture briefly. Put it into a greased and flour-dusted square springform pan (24 x 24 cm) and smooth it down.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 20 minutes. Remove the cake from the edge of the mould, let it cool lukewarm, remove the base from the bottom of the mould, but leave it on the bottom.
Soak gelatine in cold water. Wash, clean and halve the strawberries. Whip cream until stiff. Mix mascarpone, quark and 150 g sugar. Squeeze out the gelatine, dissolve, stir in 2 tbsp. mascarpone quark mixture and quickly stir into the remaining mascarpone quark mixture.
Fold in the cream. Place the edge of the cake tin around the base and spread about half of the cream on the cooled base. Spread strawberries on top.
Mix the cake glaze and 2 tablespoons of sugar in a small saucepan, stir gradually with 250 ml of cold water using a stirring spoon until smooth. Bring to the boil while stirring. Immediately spread the glaze evenly over the strawberries.
Fill the remaining mascarpone cream in portions into a piping bag. Spread the cream in tuffs over the strawberries. It is better to keep it cold overnight for at least 4 hours. To serve, dust with cocoa and cut into pieces.