Preheat the oven to 350°. Season the duck breast with salt and pepper. In a small ovenproof skillet, cook the breast, skin side down, over low heat until the skin is golden brown, about 15 minutes; pour off the fat as it accumulates in the pan. Turn the duck breast over and transfer the skillet to the oven. Roast the breast for about 10 minutes, until an instant-read thermometer inserted in the thickest part registers 135°. Let the duck breast rest for 10 minutes, then slice it very thinly across the grain.