Rossini Burger | Saveur

Ingredients

• 2 lb. ground beef
• Sea salt and freshly ground black pepper, to taste
• 1 tsp. cornstarch
• 1 cup hot veal demi-glace
• 2 tbsp. extra-virgin olive oil
• ¹⁄₄ cup madeira or red wine
• 4 tbsp. unsalted butter, at room temperature
• 4 truffled brioche buns or hamburger buns
• 10 oz. duck foie gras, sliced into 1/2"-thick slabs and chilled
• 1 oz. black truffle, thinly sliced