Rich and concentrated, demi-glace is well worth the time it takes to make it. Browning bones and vegetables in a roasting pan in the oven before combining them in a pot with water gives this stock a more pronounced flavor and deeper color. Veal bones have more collagen than beef bones; simmering the bones transforms the collagen into gelatin, which makes for a thicker, richer stock. At Le Ferrandi and many French restaurants, they leave celery out of their stocks, as they believe the flavor to be too assertive. Demi-glace can be swirled into soups and stews to lend complex flavor or used as a base for countless sauces.