Drain the gooseberries on a sieve and collect the juice. Measure out 400 ml of juice. Mix sauce powder with approx. 150 ml juice (of the measured one) until smooth. Bring the rest of the juice to the boil, stir in the sauce powder and bring to the boil again briefly while stirring.
Carefully stir in the gooseberries and allow to cool slightly. Meanwhile, for the dough, mix quark, sugar, milk, oil, grated lemon rind and salt in a bowl. Mix flour and baking powder, stir in about half of the flour, then knead in the rest of the flour.
Form the dough into a 38-40 cm long roll on a floured work surface and place diagonally on a baking tray lined with baking paper. Flatten the roll to a strip of approx. 18 cm wide. Press a small rim on the left and right side.
Put gooseberries on the dough strip, brush the edges of the dough with condensed milk and sprinkle with almond flakes. Bake in the preheated oven, 2nd shelf from below, (electric oven: 200 °C/ convection oven: 175 °C/ gas: level 3) for 25-30 minutes.
Let the cake cool down on the baking tray. Serve dusted with icing sugar. Serve with crème légère.