I made this up a few weeks ago, using two grapefruit, which was a little too grapefruity and tart. This is the amended recipe - be warned, it may need further changing. Good with any fairly fatty fish - mackeral is cheap and much undervalued, I think.

Clean the mackeral. Zest the grapefruit, then juice it. Reserve 4 thin slices of peel. Add an equal quantity of gin to the juice and zest. Marinade the fish in this mixture for a couple of hours. Remove the fish from the marinade, and grill for about 5-8 minutes each side, depending on the size of the fish. (Until the flesh next to the bone is just opaque.)

Meanwhile fry the onion in the butter on a low heat until just golden. Add the marinade and sugar, and turn the heat up - simmer the sauce until it is thickish. Adjust seasoning, and thickness with orange juice / potato starch.

/Fish