Caramelizing the onions is the most important step in this recipe, as it’s the base that gives the dish its signature depth of flavor. Here’s how to get perfectly caramelized onions:

Heat a large, heavy-bottomed skillet over medium heat and add the butter and olive oil.

Once the butter is melted, add the sliced onions and a pinch of salt. Stir to coat the onions evenly.

Cook the onions slowly, stirring occasionally. After about 10 minutes, you can add the sugar to help with caramelization (this step is optional).

Continue cooking for 30-40 minutes, stirring every few minutes. The onions will become soft, golden, and deeply caramelized.

When the onions reach a rich brown color, add the garlic and cook for another 2 minutes, until fragrant.

Once the onions are caramelized, it's time to deglaze the pan with Marsala wine.

Pour the Marsala wine into the pan, stirring to scrape up the caramelized bits at the bottom of the skillet.

Let the wine simmer for about 5 minutes, until it reduces by half and the alcohol cooks off.

Now it’s time to turn those onions into a creamy, luxurious sauce.

Stir in the thyme and Worcestershire sauce.

Add the broth, followed by the heavy cream, and stir well to combine.

If you prefer a thicker sauce, whisk in the flour at this stage to thicken the mixture. Simmer for another 5-10 minutes until the sauce is velvety and smooth.

Cook the Pasta:

While the sauce is simmering, cook your pasta.

Bring a large pot of salted water to a boil and cook the pasta according to the package instructions until it’s al dente.

Reserve about ½ cup of pasta water, then drain the pasta.

Here comes the fun part—combining everything together!

Add the cooked pasta directly into the skillet with the sauce.

Toss the pasta in the sauce, ensuring each strand is coated in the rich, oniony goodness.

If the sauce is too thick, you can loosen it up with the reserved pasta water, adding a little at a time until you reach the desired consistency.

This wouldn’t be a French onion-inspired dish without plenty of cheese!

Remove the skillet from the heat and stir in the Gruyère cheese, allowing it to melt into the sauce.

Sprinkle the Parmesan over the top and stir until everything is cheesy and gooey.