How to Make It
Melt 1 tablespoon of the butter in a medium saucepan. Add the shallot and cook over moderate heat, stirring frequently, until softened, about 2 minutes. Add the port and white wine and cook over moderate heat until the sauce is reduced to 2 tablespoons, about 7 minutes. Add the raspberry preserves, vinegar and mustard and whisk over low heat until smooth. Add the raspberries and cook, whisking gently to break up the berries. Whisk in the remaining 1 tablespoon of butter and season with salt and pepper; keep the sauce warm.
Using a thin, sharp knife, make a crisscross pattern in the duck skin. Heat the oil in a large skillet. Add the duck breasts, skin side down, and cook over moderate heat until the skin is browned and crisp, 4 to 5 minutes; pour off the rendered fat as it accumulates in the pan. Turn the duck breasts and cook until the bottom is browned, about 2 minutes. Turn the duck again and cook over moderately low heat until most of the fat has been rendered, about 5 minutes longer; don't let the skin burn.
Transfer the duck breasts to a cutting board and let them rest for 5 minutes. Thinly slice the duck on the diagonal and arrange on plates. Spoon the raspberry-port sauce all around the duck and serve.