Step 1

Preheat the oven to 400 degrees F.

Step 2

Cook the pasta according to the package instructions. Drain and set aside.

Step 3

Meanwhile, heat the butter and olive oil in a large skillet over medium heat. Add the onions and garlic. Season with salt and pepper. Cook until softened, 4 to 5 minutes.

Step 4

Sprinkle over the flour and stir with a whisk as you add. Let the flour cook for 1 minute. Continue whisking while slowly pouring in the milk, then the cream. Cook until thick and bubbling, 2 to 3 minutes. Stir in the cheeses in handfuls until completely melted. Taste and adjust the seasoning as needed.

Step 5

Add the pasta and stir until completely coated. Sprinkle over the fried onions.

Step 6

Bake until the onions are deep golden and crisp, 10 to 12 minutes. Sprinkle with the green onions, if using.