1 cup Soy Sauce
1 cup Sherry
4 6-OZ duck breast halves
12 frozen dark sweet cherries, thawed and halved
1 cup chicken stock
1 cup beef stock
1/2 cup ruby port
1 fresh thyme sprig
1 TSP cornstarch dissolved into 2 TBSP water
1/4 cup butter, cut into 1/2-inch pieces
Whisk soy sauce and Sherry in medium bowl to blend. Using a sharp knife, make diagonal slits on the duck breasts 1/2-inch apart making sure to not cut too deep (not through meat). Place duck, skin side up into glass baking dish. Pour marinade over. Cover duck with plastic wrap and refrigerate at least 2 hours and up to 6 hours.
Bring cherries, chicken stock, beef stock, port and thyme spring to boil in a heavy medium saucepan over high heat. Simmer until mixture is reduced to 1/2 cup.
Meanwhile, heat heavy large skillet over medium heat. Remove duck from marinade. Add duck breasts, skin side down to skillet. Cook until skin is crispy, about 10 minutes. Turn duck over and continue cooking to desired doneness, about 5 minutes for medium. Transfer duck to cutting board or other surface.
Add cornstarch mixture to port-cherry sauce. Bring to simmer, whisking constantly. Add butter one piece at a time until melted.
Slice duck breast and fan out on plates. Spoon sauce over duck then serve.