Preheat oven to 400°F/205°C. Grease a 9x13-in. baking pan with butter and olive oil and add onions, garlic and sugar. Roast for about one hour, stirring occasionally until the onions are soft and caramelized.
In a large sauce pan or stock pot, combine cooked onions, beef stock, wine, bay leaf, thyme, salt and black pepper. Bring the soup to a low boil over medium heat. Reduce the heat and simmer for 25 - 30 minutes, stirring occasionally. Season to taste with salt and pepper. Add the lemon juice. Remove from heat and stir in the Parmesan cheese.
Preheat oven to 450°F/230°C. Position the oven rack into center of oven.
Place four mini soup pots on a baking sheet and ladle the soup into each. Arrange two slices of bread on top of each soup pot and sprinkle each with Gruyère cheese.
Bake until the cheese is golden and bubbly. Serve immediately.
Recipe was created especially for the Calphalon Enamel Cast Iron Mini Soup Pots.