Step 1

Make the French onion soup onions: Heat a large Dutch oven over medium-high heat. Add the butter and onions and stir until the butter melts. Add the salt and sugar and cover the Dutch oven with a lid. Cook for about 20 minutes, stirring occasionally.

Step 2

Once the onions are translucent and their liquids have been released, uncover, reduce the heat to medium and continue to cook and caramelize for 40 to 45 minutes. You want to make sure to deglaze with about 1/4 cup of water and scrape with a wooden spoon when the onions get very dark and start sticking to the bottom of the pan. Do this at least twice.

Step 3

Once the onions are uniformly caramelized, add the thyme and then deglaze with the sherry while scraping the fond off the bottom of the pan. Take the pan off the heat and let cool.

Step 4

For the buttery breadcrumbs: Heat a 12-inch skillet over medium-low heat. Add the butter and gently melt until foaming. Process the bread in a food processor until coarse breadcrumbs form. Add the breadcrumbs to the butter and sauté until golden, 3 to 5 minutes. Transfer to a bowl and season with salt and pepper to taste.

Step 5

For the mac and cheese: Preheat the oven to 400 degrees F. Grease a 9-by-13-inch baking dish with butter.

Step 6

Fill a large pot with water, bring to a boil and add plenty of salt. Boil the pasta until very al dente according to package instructions. Drain and fully cool.

Step 7

Set a medium saucepan over low heat and add the evaporated milk and Dijon. Whisk together until smooth and bring to a simmer. Take off the heat and add half of the Gruyère. Add the processed cheese and hot sauce and stir until the cheese is melted and the sauce is smooth. Combine the pasta with the cheese sauce and season to taste with salt and pepper if necessary. Then add to the buttered baking dish

Step 8

Sprinkle an even layer of the cooled caramelized onions over the top of the pasta. Add a nice even layer of the buttery breadcrumbs. Finally, top with the remaining Gruyère in a thick layer. Bake uncovered until the top is golden brown and bubbling, 15 to 20 minutes. Let cool for 5 minutes before slicing.