Truss the mallard with a square of pork back fat season and roast through a hot oven, 180 degrees for 15 mins or so. Remove the pork fat after ten mins to allow the breast to brown. Baste the bird every so often. Remove and rest well somewhere warm.
Sweat the shallots and thyme sprig in half of the butter for 10 mins Add the port and red wine. Reduce to almost a syrup Add the black current juice and simmer for 5 mins.
Add the whole black currents and warm gently.
Whisk in the butter and serve.
Carve the rested duck and spoon round the sauce. Serve with game chips and watercress.