Cacio e pepe is a really simple pasta to make, but often it's done incorrectly. How often have you made it and all the cheese clumps together? I'm going to show you how to avoid that, and make it the right way.
Cook the pasta and prepare the dish: Bring a large pot of water to boil; then add two large pinches of salt. Add 3 tablespoons olive oil to a saucepan over medium heat. Add the black pepper and toast until fragrant, about 2 minutes. Meanwhile, add the spaghetti to the boiling water and cook until al dente, stirring occasionally, about 3 minutes less than what the box advises. Grate the cheese and set aside.
While the pasta is cooking, pour remaining olive oil into a serving dish large enough to hold and toss the pasta. Reserve 2 cups of the pasta water: add 1 cup to the pepper-olive oil mixture, and put aside the other cup. Pour about a quarter of the pepper-olive oil-water mixture into the serving dish (to temper the dish).
Assemble the dish: When the pasta is firm to the bite, drain the pasta and add it directly to the serving dish. Add the rest of the pepper-olive oil-water mixture to the pasta. Stir vigorously with two forks so the black pepper is evenly distributed and the pasta has a chance to absorb the water; then, add half the cheese and continue tossing and stirring. The more you mix, the creamier it gets. Once the cheese has been integrated, add the remaining cheese and continue tossing until the sauce is thick and creamy and the noodles are coated evenly, another minute. (If, at any point, the sauce seizes up, simply add a touch more reserved pasta water to loosen it up.) Transfer to individual dishes, sprinkle with additional Pecorino Romano, and serve immediately.