Creamy French Onion Mac and Cheese

Preheat oven to 375ºF. Butter an 8×8 inch baking dish.

In a large skillet, melt 2 tablespoons of the butter over medium-low heat. Add onions with a pinch of salt and cook, stirring occasionally, until golden and reduced, about 40 minutes.

Bring a pot of salted water to a boil and cook pasta according to the directions. Drain and set aside.

In the same pot you used to cook the pasta, melt remaining 4 tablespoons butter over medium-high heat. Add flour, whisking until combined to create a roux. Cook for 1 to 2 minutes until golden and smooth. Slowly pour in whole milk, whisking constantly, about 5 minutes. Slowly pour in evaporated milk and whisk until thickened. Reduce heat to low and add Gruyere and Swiss cheeses and all but a couple tablespoons of the Parmesan. Stir until all of the cheese is melted. Stir in nutmeg, mustard and salt and pepper to taste. Stir in cooked pasta and onions.

Transfer mixture to the buttered baking dish and top with remaining Parmesan. Bake until top is golden brown, about 25 minutes. Cool for a few minutes before serving.