Score the Skin (Day Before Cooking): Using a sharp knife, score the duck skin in a diagonal crosshatch pattern, being careful not to cut into the meat. Alternatively, use a sausage pricker to create tiny holes across the skin’s surface. This helps render the fat more efficiently.
Dry the Skin. Place the scored duck breasts on a rimmed baking sheet and refrigerate uncovered for 8–12 hours, or up to 3 days. The cold air dries out the skin, ensuring maximum crispiness when cooked.
Bring to Room Temperature. About 30 minutes before cooking, remove the duck breasts from the refrigerator. Preheat the oven to 350°F (175°C). When ready, heat a small amount of neutral oil in a large skillet over medium heat.
Sear the Duck Breasts. Season both sides with kosher salt and black pepper. Place the duck skin-side down in the pan and cook undisturbed for 5–8 minutes, until the fat has rendered and the skin is golden brown and crisp. The duck is ready to flip when it easily lifts from the pan and the fat has visibly shrunk.
Finish in the Oven. Carefully flip the duck breasts, ensuring the skin remains intact. If using aromatics like garlic or fresh herbs, add them now. Transfer the skillet to the preheated oven and cook for 5–7 minutes. Check for doneness—135°F (57°C) for medium-rare.
Rest Before Slicing. Remove the duck from the pan and let it rest for 5–10 minutes. Slice into ¼–½ inch thick pieces while preparing the sauce.
Make the Port Cherry Sauce. Drain off all except for 1 tablespoons of the rendered duck fat, then set over medium-high heat. Sauté halved garlic, ¼ cup cherry jam, and 3 sprigs of thyme for 1–2 minutes, breaking up the jam. Pour in ½ cup Port (or red wine) and ½ cup chicken stock, then bring to a boil and reduce by half. Remove from heat, swirl in 1 tablespoon unsalted butter until melted, then serve the sauce over the sliced duck with a sprinkle of flaky sea salt.