Start by heating the butter and olive oil in a large pot over medium heat. Once the butter melts, add the sliced onions. Stir occasionally. This will take around 20 minutes. You want them to be soft and golden.

When the onions are nicely caramelized, toss in the minced garlic and stir for about a minute. You’ll smell the garlic fragrant. Be careful not to burn it.

Sprinkle the flour over the onions. Stir it all together, cooking for about 2 minutes. This will help thicken your soup later.

Gradually pour in the beef broth while stirring. It helps to scrape up any bits from the bottom of the pot. Next, add salt, pepper, brown sugar, thyme, and Worcestershire sauce.

Bring the mix to a boil, then reduce to low heat. Let it simmer uncovered for about 30 minutes. This allows all those flavors to meld beautifully.

While the soup simmers, preheat your oven to broil. Place slices of the baguette on a baking sheet and toast until golden brown.

Ladle the soup into oven-safe bowls. Add a slice or two of the toasted baguette on top, and sprinkle with cheese.

Put the bowls under the broiler until the cheese is bubbly and golden. This might take just a few minutes, so watch carefully!