Melt the butter and let it cool down a little. Grind the biscuits finely in the universal chopper and mix with butter. Lightly brush the bottom of a springform pan (approx. 26 cm Ø) with oil. Put biscuit crumbs into the mould and press them down to a smooth base. Place the mould in a cool place for approx. 30 minutes.
Wash the lime and orange in hot water and rub dry. Finely grate the zest of 1 lime and the orange. Halve the lime and squeeze it. Halve the orange and squeeze 1 half. Mix orange and lime juice with mascarpone, quark, sugar, vanilla sugar, lime and orange peel until creamy. Stir in eggs. Sift the starch over the eggs and fold in. Pour the quark mixture into the mould and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 60-70 minutes. Take out the cake and let it cool down on a cake rack
Cut the remaining limes into slices. Bring brown sugar and 75 ml water to the boil, simmer lime slices in it for 1-2 minutes in portions, remove. Boil down sugar water like a syrup. Dust the cheesecake with icing sugar and decorate with limes, sprinkle with remaining syrup as desired
waiting time approx. 3 hours