Melt butter in a dutch oven over medium-high heat. Add onions and saute, stirring every few minutes for about 30 minutes until onions are caramelized. In the last couple minutes of cooking add in minced garlic and saute until fragrant.
Stir in flour and cook for another minute. Gently pour in the wine to deglaze the pan, using the bottom of your spoon to scrape up any browned bits.
Add water, Yondu Vegetable Umami Seasoning, Worcestershire, bay leaf, and thyme sprigs. Bring the soup to a simmer and let cook for 10 minutes. Season to taste with salt and pepper.
While the soup simmers, preheat the oven to 400 degrees. Place sliced baguette on a baking sheet and drizzle with olive oil. Bake for 6-8 minutes, until the edges are golden brown.
Once the soup is done, ladle into oven-safe bowls that are placed on a baking sheet. Top each bowl with a piece of toasted baguette and about ¼ cup shredded cheese.
Switch oven to broil and place in the oven for about 3-5 minutes so the cheese will melt and be bubbly. Keep a close eye so the top does not burn.
Remove from the oven and let cool for a few minutes before serving.