Bring a large pot of lightly salted water to a boil. Add pasta and cook according to package directions. Drain and set aside.
Melt butter in a large saucepan over medium heat. Add flour, salt, pepper, ground mustard, and paprika. Cook, whisking constantly until smooth, 1 to 2 minutes.
Gradually whisk in whole milk and heavy cream. Cook, whisking constantly, until sauce is thickened and bubbly, 5 to 7 minutes.
Reduce heat to low. Add cheddar cheese and Gruyère cheese; stir until melted and smooth. Add cooked pasta and stir until evenly coated. Serve immediately.
