In a heavy pot over medium heat, melt butter and olive oil together. Add thinly sliced yellow onions, season with salt and pepper, and cook for about 45 minutes, stirring occasionally, until they turn golden brown and jammy.

Once the onions are beautifully caramelized, stir in brown sugar and cook for an additional 2 minutes. Add white wine (if using) and scrape up any flavorful brown bits from the pot.

Pour in vegetable or beef broth along with thyme and bay leaves. Simmer for 15 minutes.

Preheat your oven to 425°F (220°C).

Add the gnocchi to the simmering broth and cook until they begin to float, about 3-4 minutes.

Remove thyme stems and bay leaves. Stir in half of the Gruyère cheese and all of the Parmesan until melted.

Transfer the mixture to a baking dish. Top with the remaining Gruyère before baking.

Bake for 15-20 minutes, or until the top is golden brown and bubbly.

Allow to rest for 5 minutes before serving.