Add the stock, worcestershire sauce (optional), bay leaf, and thyme. Bring to a simmer. Then reduce heat to medium-low and simmer for at least 10-15 minutes, partially-covered. Season to taste with salt and pepper. Discard the bay leaf and sprigs of thyme.
Preheat oven to 400 degrees F. While the soup is simmering, slice the baguette into 1-inch thick pieces and arrange them in single layer on baking sheet. Bake for 6-8 minutes, until the bread is toasted and golden around the edges. Remove and set aside.
Switch the oven to the broiler. When ready to serve the soup, place your oven-safe bowls or crocks on a thick baking sheet. Ladle the soup into each of them, then top with a baguette slice and your desired amount of cheese (I used about 1/4 cup shredded cheese for each). Place on an oven rack about 6 inches from the heat and broil for 2-4 minutes until the cheese is melted and bubbly. Remove and serve immediately.
*If you do not have access to a broiler or would like to save time, I also love just topping this soup with croutons and shredded cheese.