Cook pasta according to package directions, drain and place into a large bowl.
In a large saucepan over medium heat, melt butter. Cook minced garlic in it until fragrant. Add in flour and ranch seasoning mix and cook it for a minute to brown.
Pour in the milk and add in both of the cheeses. Continue to cook over medium heat, while whisking constantly until the cheeses have melted and the sauce has thickened.
Pour the sauce over the pasta and mix until fully combined.