Scale and fillet the red mullet. Remove the line of small bones that runs down the middle of the fillets.
Top and tail the gooseberries and cut them up small. Place in a pan with the syrup and half of the white wine, bring to the boil and simmer until soft. When soft, purée them in a blender or food processor, then pass through a sieve.
Bring the remaining wine and the fish stock to the boil in a saucepan and reduce until syrupy. Add the veal stock, bring back to the boil and reduce slightly until it starts to thicken.
Season the fillets only on the meat side. Heat a little oil and half the butter in a frying pan until it sizzles. Place the fish, skin side down, in the pan and fry gently for about 20 seconds, then turn and finish cooking on the meat side for 1 minute. When cooked, remove the fish and drain on kitchen paper to remove any excess fat. Cover and keep warm.