Bring a large pot of salted water to a boil. Add the spaghetti and cook until al dente according to package directions.
Before draining, reserve at least 3/4 cup pasta water.
Drain the pasta and immediately return it to the warm pot or transfer it to a large skillet over low heat.
Add 1/4 cup Challenge Sea Salted Butter in a Tub and 1/2 cup reserved pasta water. Toss until the butter melts and coats the pasta.
Add the Parmesan and black pepper. Toss vigorously until the cheese melts and a smooth, glossy, creamy sauce forms. Add more reserved pasta water a little at a time as needed, up to 3/4 cup total.
Remove from the heat and taste. Add another scoop or two of butter if you’d like it even richer and more buttery.
Divide among bowls and finish with additional Parmesan and freshly cracked black pepper.