Put the rusks in a freezer bag and crush them finely with a cake roll. Melt the fat and mix with 1 tablespoon of sugar, vanillin sugar and the rusk crumbs. Line a box form (30 cm long) with foil so that it protrudes over the edge.
Pour the crumb mixture into the box mould and press down firmly. Put it in a cold place. Soak gelatine in cold water. Beat the mascarpone and yoghurt with lemon juice, zest and remaining sugar with the whisk of the hand mixer until foamy.
Squeeze the gelatine, dissolve carefully. First mix 2 tablespoons of the mascarpone cream with gelatine. Stir the mixture into the remaining cream. Pour onto the crumb base. Smooth the surface.
Chill for about 2 hours. Clean, wash, halve and seed the grapes. Carefully lift the cake out of the mould using the foil and cut it into 8 pieces. Colourfully cover the slices with the grapes.
Melt apricot jam at low heat, pass through a sieve and drizzle over the grapes. Results in about 8 slices.