1. Heat the margarine in a large saucepan and saute the sliced onions for about 5 minutes at high temperature.
2. Reduce the heat and leave the onions to caramelize for about 15 minutes, stirring from time to time.
3. When you notice a caramelized deposit on the bottom of the saucepan, stir in the flour and increase the temperature.
4. Cook for 3-4 minutes and deglaze with the white wine.
5. Add the brown beef stock and the bay leaves and boil for 20 minutes.
6. Season the French onion soup to taste with salt and pepper.
Cooking tip: If you do not have brown beef stock use beef au-jus on powder diluted with water.
7. Toast the baguette slices in the oven until crispy.
8. Pour the soup in oven-proof soup crocks and float a couple of baguette slices on top of each soup.
9. Place some sliced Gruyere cheese on top of the bread and bake the soups until the cheese is melted.
Tip: Although Gruyere cheese is originally used for the French Onion Soup, many cooks use Swiss cheese instead.