French Onion Soup

This is one of my favorites.  The recipe calls for Gruyere cheese but I have made French onion soup with Swiss, Provolone and Fontina as well as Gruyere. 

1/4 C. unsalted butter, more for the baking sheet
4 medium-large yellow onions, thinly sliced
Kosher salt and freshly ground pepper
1 tsp. granulated sugar
1 small baguette, cut into 1/2 inch slices
2 quarts homemade beef broth or low sodium beef broth
1 bay leaf
2 C. Gruyere

Melt the butter in a 4 quart pot over medium heat.  Stir in the onions and season with 1 tsp. salt and a few grinds of pepper.  Reduce the heat to low.  Press a piece of foil onto the onions to cover them completely, cover the pot with a lid and cook, stirring occasionally, until the onions are very soft but not falling apart, 40 to 50 minutes.  Remove the lid and foin, raise the heat to medium high and stir in the sugar.  Cook, stirring often, until very deeply browned, 10 to 15 minutes.

Meanwhile, make the croutons.  Position the rack in the center of the oven and preheat to 350 degrees.  Butter a rimmed baking sheet and arrange the baguette slices on the sheet in a single layer.  Bake until the bread is crisp and lightly browned, turning once, 15 to 20 minutes.  Set aside.

Add the broth and bay leaf to the carmelized onions and bring the soup to a boil over medium high heat.  Reduce the heat to medium low and simmer for 10 minutes to blend the flavors.  Discard the bay leaf and season to taste with salt and pepper.

To serve, position the oven rack 6 inches from the broiler and heat the broiler to high.  Put broilerproof soup bowls or crocks on a baking sheet.  Put 2 or 3 croutons in each bowl and ladle the hot soup on top.  Sprinkle the cheese on top and broil until the top is browned and bubbly, 2-5 minutes.  Serve immediately.