1. Cut the fish into 4 fillets Leave the skin on the fillets to help keep them in shape.
2. Heat the butter in a heavy frying pan and cook the fillets gently on both sides for 2 minutes.
3. Turn down the heat, add the wine and cook gently for another 10 minutes.
4. Transfer the fish to a warm serving dish.
5. Reduce the liquid, cool slightly, stir in the quark and season to taste with salt and pepper.
6. Pour over the fillets and serve immediately with tiny new potatoes and with a side salad, if liked.