French Onion Mac and Cheese

Preheat the oven to 425 degrees F. Butter a 2-quart baking dish.

Bring a large pot of salted water to a boil

Melt the butter with the oil in a large skillet over medium-high heat. Add the onions and 1 teaspoon salt and stir to coat thoroughly.

Reduce the heat to medium and cook covered, stirring every few minutes, until the onions are very soft and golden, about 20 minutes.

Uncover, increase the heat to medium high, and cook, stirring constantly, until golden brown, about 5 minutes more. Sprinkle the flour on top and stir until absorbed.

Gradually add the beef broth, stirring well to incorporate the flour as you go. Stir in the cream and bring to a simmer. Simmer until slightly thickened, about 3 minutes.

Cook the elbows according to package directions, using the lower end of the cooking time range. Return the elbows to the pot and add the hot onion mixture and 1 cup of the gruyere the mozzarella; toss to coat.

Transfer the mixture to the buttered baking dish and sprinkle with the remaininging cup of gruyere. Bake until the cheese on top is melted and browned in spots, about 20 minutes.