Bring a large pot of water to a boil. Salt the boiling water and add the spaghetti. Cook until just shy of al dente according to package instructions, about 10 minutes.

When the pasta is done cooking, ladle out ½ cup of the starchy cooking water into a small bowl, and then drain the pasta.

In a large skillet, bring about 1 ½ cups of water to a boil.

Whisk the cornstarch into the reserved cooking water to make a slurry. Then whisk this slurry into the boiling water in the skillet. Add the cheese and cook until the sauce thickens, about 3-4 minutes, whisking often. If the sauce doesn't seem like it's coming together, mix another teaspoon of cornstarch with a little extra water and add it, while continuing to whisk.

Off heat, toss the pasta with the cheese sauce and desired amount of freshly ground black pepper until well coated. Serve with additional freshly grated Pecorino Romano cheese and freshly ground black pepper.