Step 1

In a large skillet, add butter and oil over medium low heat. Once butter is melted, add sliced onions and salt and cover with a lid. Cook for 5 minutes, or until onions begin to lightly sweat. Uncover and toss onions to incorporate melted butter. Cook uncovered for 1 hour, stirring frequently, being sure to scrape the bottom and sides of pan. Deglaze with a splash of stock about every 15 minutes, incorporating the browned bits back into the onions. Onions should be a deep brown color with a marmalade-like consistency.

Step 2

Twenty minutes before onions are done cooking, bring a large pot of water to a boil and assertively salt. Add fusilli and cook until al dente, according to package instructions. Drain and reserve.

Step 3

Once onions are deeply caramelized, reduce heat to low. Add flour and cook for an additional 2 minutes, stirring frequently, or until flour is fully incorporated and lightly cooked.

Step 4

Add whole milk, heavy cream, mustard, thyme and black pepper and stir to combine. Bring to a simmer then cook for 6-8 minutes, or until thick enough to coat the back of a spoon and when a line is drawn through the sauce, it stays. Sprinkle small handfuls of provolone and Gruyere and stir until melted. Repeat until all cheese has been incorporated.

Step 5

Add cooked pasta and gently stir to combine. Reduce heat to low and keep warm while making breadcrumbs.

Step 6

Preheat oven to broil.

Step 7

While oven is preheating, spread a thin layer of butter on each baguette slice. Equally divide cheese between each slice of bread, then top with a sprinkling of thyme leaves.

Step 8

Broil for 2-3 minutes, or until bread is golden brown and crunchy all the way through. Remove from oven and allow to cool for a few minutes.

Step 9

Cut bread slices in half and add to the bowl of a food processor. Process for about 30 seconds, or until breadcrumbs are a mixture of medium and fine sized.

Step 10

Spoon the mac and cheese into serving bowls and top with breadcrumbs.