In a heavy bottom large pot, melt the butter over medium heat.
Whisk in the flour and cook for about 1-2 minutes until well combined and smooth.
Gradually whisk in the half and half, making sure there are no lumps.
Cook the mixture for about 5-7 minutes, stirring constantly, until it thickens and comes to a simmer.
Reduce the heat to low and stir in the shredded white cheddar cheese, salt, black pepper, and mustard powder. Mix until the cheese is melted and the sauce is smooth and creamy.
Add the cooked cavatappi pasta to the pot and stir until the pasta is evenly coated with the cheese sauce.
Taste and adjust the seasonings to your liking.
Serve the mac and cheese hot and enjoy!
