Melt butter in large skillet over medium high heat. Slice onions into fine rings and fry on low heat til soft and golden brown. Stir occasionally to keep onion slices from sticking. Add the stock and blend in . Gradually add the flour and blend again. Let cook for 20 minutes. Add salt to taste
Place toasted bread pieces in ovenware soup bowls. Pour cooked onion stock over bread. Garnish with grated Fontina cheese. Put bowls in oven at 180 degrees til cheese is melted. Makes 4 servings.