Step 1

Using a sharp knife, make diagonal cuts along the skin of the duck, but be careful not to cut into the breast itself. Rotate the breast and score the skin another time. This will make a diamond-shaped pattern on the duck skin.

Step 2

In a resealable bag or large bowl, combine orange juice, white wine vinegar, rosemary, garlic, salt, pepper, and brown sugar. Add duck breasts, seal the bag or bowl, then refrigerate for 3-4 hours, up to overnight.

Step 3

Light charcoal in a half-full chimney starter, and heat until the edges are gray (about 10 minutes).

Step 4

Add charcoal to grill, place cooking grate on top, and preheat for 5-7 minutes with the draft door closed.

Step 5

While the grill is preheating, place a melting pot on the grate and add butter. Once melted, add garlic and simmer for 2-3 minutes.

Step 6

Add remaining sauce ingredients, except the cornstarch, and stir until incorporated. Continue stirring frequently until the sauce has reduced by ¼ cup. Stir in the cornstarch, then remove from heat—the sauce should thicken slightly.

Step 7

Remove duck from the marinade and pat dry. Oil the grill grate, add the duck breasts skin-side down, and cook for 5-7 minutes. Watch for flareups—duck skin is very high in fat. Move the breasts around the grill to avoid direct contact with flames.

Step 8

Flip the breasts and continue to cook until the duck is cooked to your desired temperature is reached, about 10–15 minutes.

Step 9

After the first flip, place oranges on the grill cut-side down. Grill until nicely charred, about 5 minutes.

Step 10

Remove duck from the grill and cover with foil. Allow the duck to rest for 5 minutes before slicing.

Step 11

Slice the duck and drizzle with sauce. Serve with grilled oranges.