Preheat your oven on 200 degrees.
Butter the base of a 9 inch cake tin or similar and line with baking paper.
Blend the biscuits to crumbs and place in a mixing bowl.
Melt the margarine in a saucepan and stir in to the biscuit crumbs until mixed well.
Transfer the crumbs to the lined cake tin and press down with the back of a spoon.
In another mixing bowl, mix together the eggs and quark (and vanilla and sweetener if using plain quark).
Pour on top of the biscuit crumbs and smooth if needed to make level.
Place in the oven for 30-40 minutes until set, but if browning on the egdes too soon, cover the top with some tinfoil until the time is up.
Remove from the oven until cooled and place in the fridge until completely cold and serve.