Bring 3 quarts water to a boil in a large pot. Season with salt; add pasta and cook, stirring occasionally, until about 2 minutes before tender. Drain, reserving 3/4 cup pasta cooking water.
Melt 2 Tbsp. butter in a large heavy skillet over medium heat. Add pepper and cook, swirling pan, until toasted, about 1 minute.
Add 1/2 cup reserved pasta water to skillet and bring to a simmer. Add pasta and remaining butter. Reduce heat to low and add parmesan, stirring and tossing with tongs until melted. Remove pan from heat; add Pecorino, stirring and tossing until cheese melts, sauce coats the pasta, and pasta is al dente. (Add more pasta water if sauce seems dry.) Serve immediately.