Slice the yellow onions thinly with the grain.

In a large pot, combine olive oil and unsalted butter over medium heat. Once melted, add sliced onions and cook uncovered for about 10 minutes.

Sprinkle the onions with granulated sugar and continue to cook uncovered for 30-40 minutes until browned.

Add minced garlic and sauté for 1 minute.

Pour in the dry sherry wine to deglaze the pot and cook until evaporated.

Add beef stock, bay leaf, fresh thyme, and salt. Bring to a simmer for about 30 minutes.

Taste and adjust salt and black pepper as needed.

Brush baguette slices with olive oil and toast in a preheated oven at 400°F for 6-8 minutes.

Sprinkle half of the shredded Gruyere cheese over the toasted baguette slices and broil for an additional 2-3 minutes.

Ladle soup into bowls, top with cheesy toasts, and sprinkle remaining Gruyere cheese.