Crispy Duck Breasts With Port-Cherry Reduction

1 cup best-quality soy sauce
1 cup sherry
4 6-ounce duck breast halves
12 cherries, halved (thaw, if using frozen)
2 cups chicken stock, low sodium if using canned
1/2 cup port
1 fresh thyme sprig
1 teaspoon cornstarch
2 teaspoons water
2 tablespoons butter, cut into 1/2-inch pieces, room temperature

1. Combine soy sauce and sherry in medium bowl
2. Set aside
3. Using sharp knife, score the duck the breasts in diagonal cuts at 1/2-inch intervals in duck skin (not through the meat)
4. Place duck, skin side up, in glass baking dish
5. Pour marinade over
6. Cover duck with plastic wrap and refrigerate at least 2 hours and up to 4 hours
7. Bring cherries, chicken stock, Port and thyme sprig to boil in a medium saucepan over high heat
8. Simmer until mixture is reduced to 1/2 cup, about 15 minutes
9. Meanwhile, heat a heavy large skillet over high heat
10.Remove duck breasts from the marinade
11.Discard the marinade
12.Without crowding, add duck breasts, skin side down, to skillet
13.Cook until skin is crispy, about 10 minutes
14.Turn duck over and continue cooking to desired doneness, about 5 minutes for medium
15.Transfer duck to a clean cutting board to rest
16.Combine cornstarch and water to make a slurry
17.Add cornstarch mixture to Port-cherry reduction
18.Bring to simmer, whisking constantly
19.Add butter a little at a time, whisking until butter combined before adding next piece
20.Taste and adjust for seasoning with salt and pepper
21.Slice duck breasts thinly on diagonal and fan out on plates
22.Spoon Port-cherry sauce over duck and serve