Use a sharp knife to score the duck skin in an even cross-hatch fashion. Season all over with salt and pepper.
Place the duck in a cold sauté pan, skin side-down, and then set over high heat. After about 1 minute, once the sizzling starts to intensify, reduce the heat to medium. Apply mild pressure with your spoon to the back of the duck breast and place a weight (such as a heavy heat-proof container or smaller pan) on top. Continue to cook, weighed down, for about 7 minutes. Once the fat renders, pour some out into a heatproof container. Rotate the duck and check the skin for doneness. Remove the weight and rotate the duck onto the edge of the pan to sear each side for about 1 minute. Now flip over and cook for another 2 minutes, rolling around gently to get an even sear.
Remove the duck from the pan and place on a baking rack to rest for about 5 minutes. Slice to desired thickness and serve.