Peel the mango and cut into thick slices as neatly and uniformly as possible. Simmer the slices slowly, covered, with the sugar, brandy or water, and lemon juice, for about 5 minutes, until tender but still firm and not mushy. Drain and reserve the juice.

Heat the sugar in a small saucepan over low heat until the sugar melts and caramelizes--do not let it get too dark. Remove from the heat and add the vinegar, keeping your face away from the pan. Add the demiglaze and the juice from the mangoes. Simmer until all the caramel has dissolved and the sauce is reduced slightly. Add the jelly. Adjust the seasonings with salt, pepper, and lemon juice. (Note: If the sauce is too thin, you can thicken it with a little cornstarch dissolved in cold stock.)

Season the ducks inside and out and truss them for roasting.

Brown the ducks well on all sides in hot oil. As often as necessary, drain off the fat as it renders and accumulates in the pans.

Roast the ducks at 375°F until done. Do not overcook.

Optional step: The ducks may be glazed during the last 5 or 10 minutes of roasting time. Make an extra quantity of sauce (about 4 oz or 125 ml per duck). Place the ducks on clean pans and baste them often with this extra sauce until they take on a shiny glaze.

Let the ducks stand in a warm place while you finish the sauce. Degrease the roasting pans and deglaze them with stock or wine. Strain the liquid into the sauce.

Carve the duck by cutting off the legs, cutting apart the thigh and drumstick, and slicing the breast.

For each portion, spoon a little of the sauce onto the plate. Top with some of the breast and some of the leg. Arrange a few warm mango slices around the duck.