Bring a 12-quart pot of heavily salted water to a boil over high heat.
Cook spaghetti in the boiling water, stirring occasionally, until tender yet firm to the bite, about 12 minutes.
Drain pasta, reserving 2 cups of cooking water.
Return pasta and cooking water to the pot over low heat.
Add cheese, butter, and pepper.
Stir until cheese has melted and formed a creamy sauce, about 5 minutes. Season with salt.
Serve with additional cheese, if desired.