Sauté onions and carrots (always in about equal quantities) in the butter for about 30 minutes. Stir in sugar the last 10 minutes of cooking. Increase heat so vegetables will caramelize, but do not let them burn. This gives the rich brown color to the sauce.
Stir in flour. Stir-cook for about 3 minutes. Lightly brown flour, then add stock, garlic, bouquet gar