Step 1

Preheat oven to 400°F. Lightly spray a 9x13 baking pan with non-stick cooking spray.

Step 2

Bring a large pot of water to a boil and add ½ tbsp of kosher salt. Cook the pasta according to package directions, cooking 2 minutes less than directed. Drain and rinse briefly with cold water. Set aside.

Step 3

In a large pot, melt butter. Add onions, cooking until soft and translucent, 3-4 minutes. Add garlic, dry mustard and cayenne and cook until fragrant, 30 seconds - 1 minute. Add flour, whisking constantly for 1 minute.

Step 4

Slowly add the chicken broth and whole milk, whisking constantly, until flour mixture is completely incorporated. Bring to a simmer and cook, stirring OFTEN, until slightly thickened, 15-20 minutes. Thickness Test: When you draw a finger through the sauce across the back of spoon, the sauce should hold the line with no drips.

Step 5

Remove the sauce from the heat. Gradually whisk in the cheese, one type at a time, until fully melted. This may take a few minutes. Season with pepper and salt (if needed). Using an immersion blender, blend the sauce for 1-2 minutes until it is completely smooth.

Step 6

Briefly rinse the noodles to help them separate. Pour noodles into the sauce, mixing until well combined. Pour pasta into the prepared pan and bake until hot and bubbly, about 30 minutes. Enjoy!