Preparation Put a large shallow flameproof roasting pan in middle of oven and preheat to 400°F. Pat duck dry and trim off any excess fat. Score skin in a crosshatch pattern at 1/2-inch intervals with a sharp knife, then season with 1 tsp salt and 1/2 teaspoon pepper (total). Roast, skin side down, in hot pan until an instant-read thermometer inserted diagonally into center registers 125°F, 20 to 25 minutes. Turn on broiler. Turn duck skin side up. Broil 4 to 6 inches from heat until golden brown, about 2 minutes. Transfer duck to a cutting board and let rest (skin side up) 10 minutes. While duck rests, pour off all but 1 tablespoon fat from pan, then add shallots and garlic and saué over medium-high heat until golden brown, about 2 minutes. Add sugar and cook, stirring, until dissolved. Stir in vinegar, scraping up brown bits. Add demi-glace and bring to a simmer. Stir in half of raspberries. Force sauce through a fine-mesh sieve into a small saucepan, discarding solids. Skim off excess fat. Over low heat, swirl in butter. Remove from heat and add remaining raspberries. Slice duck and serve with sauce.