Step 1

Melt the butter in a large Dutch oven. Add the onions and toss to coat in the butter, then allow to cook and caramelize over medium heat (reduce the heat if the onions start browning too quickly). Cook for 45-60 minutes, stirring every 5 minutes.

Step 2

Once the onions have caramelized, add the salt, wine, and sherry to the pot and allow everything to come to a boil. Stir in the flour and allow the mixture to thicken for a couple of minutes.

Step 3

Add the broth to the onion mixture and allow it to come to a boil. Add the uncooked pasta and cook until al dente, about 10 minutes.

Step 4

Stir in the black pepper, the thyme leaves, and ½ of the grated gruyere cheese.

Step 5

Combine the melted butter and panko bread crumbs in a small bowl.

Step 6

Sprinkle the rest of the gruyere cheese over the top, along with the buttered breadcrumbs.

Step 7

Place the entire dish under the broiler on high for 2-3 minutes, or until the cheese has melted and the breadcrumbs have slightly browned. Sprinkle extra thyme over the top of the dish.