Ingredients:

Directions:

1. Bring a large pot of water to a boil and salt it. Meanwhile, bring the butter to room temperature (you can soften it in a microwave, but don’t melt it). Put it in a warm bowl.
2. Cook the pasta until tender but not mushy; drain it, reserving some of the cooking water. Toss the pasta with the butter, adding a little of the water if necessary to thin the sauce. Toss with the Parmesan, sprinkle with salt and pepper, and serve immediately, passing additional Parmesan at the table.

Variations:
Pasta with Butter, Sage, and Parmesan. A classic when made with browned butter, almost as good with olive oil: Heat 4 or more tablespoons butter with 20 or 30 fresh sage leaves over medium heat for about 3 minutes; the butter should brown and the sage sizzle. Toss the cooked pasta with the butter, sage, and Parmesan, thinning the sauce with pasta-cooking liquid if necessary.

Pasta with Butter, Parmesan, Cream, and Vegetables. With just enough cream to lightly coat the pasta: Use 4 tablespoons (1/2 stick) butter. In Step 1, when the butter has reached room temperature, whisk in 1/2 cup heavy cream. Proceed with the recipe, adding up to 1 cup peas (fresh or thawed frozen) or cooked and chopped spinach, asparagus, or other tender cooked vegetables at the last moment.

Pasta with Butter, Parmesan, and Italian Ham. Cut about 6 ounces pancetta, coppa, or prosciutto into 1/4-inch dice. Put 2 tablespoons of the butter and the meat in a skillet over medium-high heat and cook until the meat is lightly crisped, about 5 minutes. Add this to the warm bowl with the remaining 2 tablespoons butter and proceed with the recipe.

Fettuccine Alfredo. Reduce the butter to 2 tablespoons and melt it gently. Use fettuccine. While the pasta cooks, whisk 2 eggs with 1/2 cup heavy cream and 1 cup grated Parmesan in a warmed bowl. Sprinkle with pepper. When the pasta is cooked, toss it with the cheese-egg-cream mixture, adding a little of the cooking water if necessary to keep the mixture moist. Drizzle with the butter, toss well, and serve immediately.

10 Additions to Pasta with Butter and Parmesan
Add one or a combination to the basic recipe or any of the variations.

Any chopped fresh herb of your choice or a mixture of herbs; mint is especially nice, about 1/2 cup or so
About 1 cup cooked peas
1/4 cup chopped toasted almonds or pistachios
Up to 2 cups cooked and drained broccoli florets
2 or 3 large cooked artichoke hearts, sliced
A tablespoon or so grated lemon or orange zest
A tablespoon or so salted or brined capers
Ground dried or dried and smoked chiles, like ancho, chipotle, or guajillo, to taste
2 to 4 sunny-side-up fried eggs, roughly chopped, or poached eggs (toss with the pasta)
10 to 20 mashed roasted garlic cloves

Source: https://markbittman.com/recipe/spaghetti-with-butter-and-parmesan/