In a large pot of boiling salted water, cook pasta until al dente. Reserve 1 cup pasta water; drain pasta, and set aside (reserve pot).
In pot, melt butter over medium heat. Add half-and-half and cheeses; stir to combine, and bring just to a simmer. Add pasta, and toss to combine. If needed, gradually add enough reserved pasta water to thin sauce (sauce will thicken as it stands). Serve sprinkled with parsley.