Melt butter, mix well with muesli and 2 tablespoons of sugar. Spread the bottom of a square springform pan (24 cm x 24 cm) thinly with oil. Spread the muesli mixture on the base and press it down to an even base. Chill for about 30 minutes.
Soak gelatine in cold water. Sort the berries. Wash blueberries and dab dry. Carefully mix berries with jam. Wash lime hot, grate dry and finely grate peel. Halve the lime and squeeze the juice.
Stir curd, mascarpone, sugar, lime juice and zest until smooth. Whip cream until stiff. Squeeze out the gelatine, dissolve and mix with some quark cream. Then stir into the remaining cream and fold in the cream. Spread the quark cream on the muesli base and spread loosely. Spread the berries on the cream and press in lightly. Chill the cake for about 3 hours.