In an 11-inch skillet, combine 2 tablespoons of olive oil and 2 tablespoons of salted butter over medium heat. Allow the butter to melt completely, creating a rich base. Once melted, add 2 pounds of thinly sliced yellow onions to the skillet.

Stir the onions every few minutes, keeping the heat low to encourage even caramelization. This process will take about 45–60 minutes, until the onions turn deep golden brown. If they start to stick, add 1.5 teaspoons of water occasionally.

In the last 5 minutes of caramelizing the onions, stir in 1.5 tablespoons of fresh thyme and 6 cloves of minced garlic, cooking until fragrant for 1-2 minutes.

Pour in 0.5 cup of dry white wine and allow it to reduce for 3-4 minutes, scraping any bits off the bottom of the skillet. Once reduced, sprinkle in 2.5 tablespoons of all-purpose flour, stirring well to eliminate lumps.

Mix in 2.5 teaspoons of Dijon mustard and 1 teaspoon of Worcestershire sauce. Gradually pour in 2.5 cups of low sodium beef stock, adding a bay leaf. Bring the mixture to a boil, then reduce to a simmer for 6-7 minutes until the sauce thickens.

In a medium pot of salted water, bring to a boil and add 24 ounces of gnocchi, cooking until they float (about 2-3 minutes). Drain and fold into the sauce.

Spread 1.5 cups of Gruyère cheese and 0.5 cup of Parmesan cheese evenly over the gnocchi. Preheat the broiler and place the skillet under it for 3-5 minutes until the cheese is melted and bubbly.

Remove the skillet from the oven and let it sit for a minute. Garnish with additional thyme leaves and serve immediately.