Preheat oven to 400 degrees.

Melt butter in a heavy soup pot or Dutch oven over medium-low heat. Add onions and cook, covered, for 20 minutes. Place soup pot into the oven with the lid slightly ajar to ensure the onions will brown. Allow onions to cook in the oven for 1 hour, stirring at least once during the cooking process so onions won’t stick and burn.

Remove pot from oven and place back on stovetop over medium heat. Stir, scraping off all the brown, flavorful bits. Turn off heat and pour in wine. Turn heat back to medium. Cook wine for five minutes, allowing it to reduce. Add broths, Worcestershire Sauce and minced garlic and reduce heat to low. Simmer for 30 to 45 minutes.

Butter one side of the bread slices and broil over low heat, allowing bread to brown and become crispy.
When soup is ready, ladle into bowl or ramekin. Place crispy bread on top, and then sprinkle generously with grated cheese. Broil until cheese is melted and bubbly.

Serve immediately.