Spicy French Onion Soup with Chorizo

In a large pot or Dutch oven, heat olive oil and butter over medium heat. Add the sliced onions and cook, stirring occasionally, until they are deeply caramelized and golden brown (about 30-40 minutes). This is the most important step, so be patient and don't rush it.

Add the crumbled chorizo and minced garlic to the caramelized onions. Cook for another 5 minutes, stirring occasionally, until the chorizo is cooked through and slightly browned.

Deglaze the pot with sherry (or white wine), scraping up any browned bits from the bottom. Let the sherry reduce for about 2 minutes.

Add the beef broth, thyme, bay leaf, and red pepper flakes (if using). Bring to a simmer, then reduce heat to low, cover, and cook for 15 minutes to allow the flavors to meld.

Remove the bay leaf and season with salt and pepper to taste.

Preheat your oven to broil.

Ladle the soup into oven-safe soup pots or bowls.

Top each bowl with a slice of crusty bread, ensuring it's fully submerged in the soup.

Generously sprinkle shredded Gruyere cheese over the bread.

Place the soup pots on a baking sheet and broil in the oven until the cheese is melted, bubbly, and lightly browned (about 2-5 minutes). Watch carefully to prevent burning.

Remove from the oven and let cool slightly before serving. Be careful, the bowls will be hot!