Rinse ducks, pat dry and remove excess fat from body cavities. Truss the birds. Arrange them, breast side up, several inches apart on a rack set over a large roasting pan.
Let them dry, chilled but uncovered, for 3 days. In a bowl, combine the Scotch, ginger root, garlic, zest, coriander, peppercorns, soy sauce, honey and brown sugar. Let this mixture stand, covered and chilled, for 3 days. Stir marinade and press it through a fine sieve into a small bowl.
Keeping the ducks chilled, brush them with some of the marinade, every 30 minutes, for 2 1/2 hours. Let the ducks dry at room temperature for 30 minutes. Stuff each duck with one of the bread slices, 1 scallion and 1 parsley sprig. Spoon remaining marinade into the cavities. Prick the ducks, except for the breast area, with a fork. Pour the beer into the roasting pan. Roast the ducks on the rack in the lower third of a preheated 350° F oven for 30 minutes. Tent birds with foil and roast for 30 minutes more. Discard foil and roast for another 30 minutes or until a meat thermometer registers 180° F.
The skin should be very mahogany colored and crisp. Remove stuffing ingredients with a spoon and discard them and the pan juices. Pour the juices from the cavities through a fine sieve into a small bowl. Skim the fat and reserve 1/4 cup of the juices. Arrange ducks on a platter and keep them warm, covered loosely.
In a saucepan, bring the stock to a boil, simmer it for 15 minutes and stir in reserved juices. Bring the mixture to a simmer. Stir arrowroot mixture and add to pan. Cook the mixture over mod-low heat, being careful not to boil, until thickened. Add salt and pepper to taste.
Transfer the sauce to a heated sauce boat. Garnish the duck with kumquats and serve with the sauce.
Servings: 4