Cook pasta according to package directions, 8 to 10 minutes. Drain and set aside.

While the pasta is cooking, heat the butter in a saucepan over medium heat until it begins to foam. Whisk in the flour until smooth and cook, whisking, for about 2 to 3 minutes. Stir in the milk and Hidden Valley® Original Ranch® Seasoning Mix and cook, stirring, until thickened, about 5 minutes. Fold in the cheese and stir until melted. Add the cooked pasta and mix well. Serve hot.