Prepare the duck: Pat duck breasts dry. Score the skin in a crosshatch pattern (don’t cut into the meat). Season both sides with salt and pepper.
Cook skin-side down: Place duck breasts skin-side down in a cold skillet. Turn heat to medium and cook 8–10 minutes, allowing fat to render and skin to crisp. Spoon off excess fat as needed.
Flip & finish: Flip breasts and cook 3–5 minutes more, until medium-rare (135°F internal). Add garlic, rosemary, and butter during the last minute for flavor.
Rest: Remove from skillet and let rest 5 minutes before slicing.
Optional sauce: In the same pan, add stock, wine (or vinegar), and fruit preserves. Simmer 3–5 minutes until slightly thickened. Serve over sliced duck.