03Heat the remaining oil in a heavy-bottom skillet. Add the duck, fat side down, and cook over medium-high heat until golden brown, about 5 minutes. Turn the duck over, lower the heat to medium and cook until medium rare, about 3 more minutes. Remove the duck and set aside. Pour the marinade into the pan. Add the remaining shallots. Simmer over high heat until reduced to 1/4 cup, about 5 minutes. Add the remaining broth and simmer until reduced to 1 cup, about 5 to 10 minutes. Strain. Set aside.04Remove the polenta from the oven. Cut into 8 wedges. Place 2 pieces on each of 4 plates. Cut the duck into thin strips crosswise and arrange around the polenta. Drizzle each plate with 2 tablespoons of sauce. Garnish with sage. Serve immediately.