1. Bring a large pot of generously salted water to a boil. Boil the pasta until before it’s al dente (2 mins less than package directions because it will finish cooking in the sauce), drain, and set aside.
2. Meanwhile, in a medium pot over medium-high heat, melt the butter, then whisk in the flour. Cook, whisking constantly, for 1 minute. Gradually whisk in the milk, 1 cup at a time, making sure each addition is fully incorporated before adding more.
3. Once all of the milk is added, whisk in the salt, pepper, cayenne, and mustard powder. Continue whisking until the sauce bubbles and thickens, 3-5 mins. Whisk in the white cheddar and parmesan until smooth.
4. Stir in the pasta and cook for 2–3 mins more, until the pasta reaches your desired tenderness. Serve topped with extra parmesan, if you like, and enjoy!
