Heat oven to 180C/fan 160C/gas 4. Line the base of a 23cm springform cake tin with baking parchment. Crush the biscuits to fine crumbs in a blender or food processor, tip into a bowl and mix in the melted butter. Press the crumbs in an even layer over the base of the tin, then bake for 10 mins until lightly browned and crisp on top. Remove and cool.
Put one third of the blueberries into a pan with 3 tbsp water, 175g/6oz of the sugar and the zest of 1 lime. Cook for 2 mins or until the berries just start to burst. Set aside and cool. Strain the juice into a small pan, set aside, and reserve the cooked berries.
Make the filling. Whizz the Quark and both creams with the remaining sugar, lime zest and all the lime juice until smooth. Sprinkle the gelatine over 3 tbsp cold water in a cup, leave until it looks spongy, then dissolve until clear, either in a microwave on defrost, or by standing the cup in a pan of water over a low heat. Beat a little of the creamy mixture with the gelatine then pour into the rest of the mixture, beating well to incorporate.
Take the cooled, cooked berries and fold lightly into the creamy mixture to create a ripple effect. Spoon onto the biscuit base and chill for at least 4 hours, or until set.
Meanwhile, cook the reserved juice for 2-3 mins until slightly syrupy. Stir in the remaining uncooked berries and leave to cool. When set, carefully remove the cake and slide onto a plate. Spoon the syrupy berries on top.