Finely grind the rusks. Carefully grease the springform pan (24 cm Ø) and wrap in aluminium foil several times. Sprinkle the base with rusk crumbs. Mix starch, sugar, vanillin sugar and lemon zest. Add quark and mix well with the whisk of the hand mixer. Stir in cream and eggs carefully. Fill a fat pan of the oven about 1 cm high with boiling water and put it into the preheated oven (electric cooker: 200 °C/ circulating air unsuitable/ gas: level 3) on the middle shelf.
Carefully pour the quark mixture onto the rusk crumbs in the springform pan, smooth it down and place it in the fat pan. Bake for about 10 minutes. Reduce heat (electric oven: 125 °C/ gas: level 1) and bake for another 55-60 minutes. Remove from the oven and let cool on a rack. Remove the cake from the edge of the springform pan with a sharp knife and place on a cake plate. Decorate as desired with sugared blueberries and slices of lime