Caramelize the onions

• Julienne all of the onions.
• Place them in a pot with olive oil over high heat and don't touch until the bottom of the pot starts to brown a bit.
• Turn the heat to medium, add a little white wine and scrape the bottom of the pot with a wooden spoon, mixing it into the onions with salt and pepper.
• Turn the heat to medium/low, add butter and rosemary, and cook the onions down until they are a rich, golden brown color.

Add the broth and simmer

• Add the chicken broth, beef broth and some water to add more liquid.
• Simmer for a bit and season to taste.

Toast the baguette

• Cut the baguette into pieces and toast them in the oven or air fryer.
• Switch the oven to low broil.

Broil with cheese

• Put the soup in an oven-safe bowl, add the toasted baguette pieces, then the Gruyère on top and place on the middle rack of the oven.
• After the cheese melts, switch to high broil and place near the top until the cheese starts to slightly burn, then take out.