In a wide heavy bottomed Dutch oven, set over medium heat, add the butter and oil. Once hot, add the onions. Let onions cook for 30 minutes, stirring frequently to prevent them from burning.
Sprinkle onions with sugar and salt, continue cooking until deep brown, about 15 additional minutes.
Add minced garlic and saute for an additional minute.
Use a wooden spoon to scoot the onions to one side of the pan. Slowly pour in the white wine to deglaze the pan. Scrape any browned bits on the bottom or sides of the pot.
Pour in stock/broth and worcestershire sauce. Add bay leaf, thyme, and ground black pepper. Bring to a boil, then reduce heat to simmer and cook, covered, for 30 minutes. Discard bay leaf.
Meanwhile, toast the bread so that it's deep golden brown. Add cheese and broil until bubby.
Once soup is done, ladle soup into a bowl and top with cheesy toast. Garnish with addtional thyme, if desired.