Caramelize the onions

• Melt the butter with the olive oil in a Dutch oven over medium-low heat.
• Add the sliced onions with a pinch of salt and cook slowly, stirring often, until deep golden brown.
• Add the garlic and cook until fragrant.

Build the soup

• Pour in the white wine and scrape up the browned bits.
• Add the beef stock, thyme and bay leaf, then season with salt and pepper.
• Simmer gently to let the flavors meld.

Cook the pasta rings

• Cook the spaghetti rings in the simmering soup (or in a saucepan of salted water) until tender.
• Drain if cooked separately, then stir into the soup.

Broil with cheese

• Ladle the soup and rings into ovenproof bowls or a baking dish.
• Top with toasted baguette rounds and a generous layer of grated Gruyère.
• Broil until the cheese is melted and bubbling.

Serve

• Serve hot straight from the oven, with extra black pepper if you like.