In a Dutch oven or pasta pot, cook the pasta in boiling water, salted water 1 minute shy of the package directions. Measure out and reserve ½ cup of the starchy pasta water then drain the pasta in a colander and set aside.

Melt the butter in the warm empty pot over MEDIUM-LOW heat. When melted, add the garlic and cook, stirring for a minute or two until fragrant. Sprinkle the flour over the butter and garlic and whisk for a minute or two.

Whisk in a splash of the milk until well combined then slowly pour in the remaining milk, whisking well as you add it. Add about 2 tablespoons of the reserved pasta water and whisk again to combine. Cook, whisking occasionally, for a minute or two to thicken the mixture.

Stir in the Parmesan, salt, and pepper. If cooked pasta is sticky, run water over it in the colander to loosen it up and then add it to the pot and toss with tongs until well combined. Add the parsley and toss again. If the mixture seems to thick, add as much additional pasta water as needed to reach desired consistency.

Remove from heat and serve immediately.