In a large pot, bring water to boil. Once water boils, add spaghetti and cook according to package instructions. Do not overcook. Reserve pasta water for later (be sure to reserve more than 1/4 cup in case you need more).
Drain pasta water. If pasta will be sitting for a while, rinse it with cold water and toss in olive oil to prevent it from sticking and getting overcooked.
While pasta is cooking, prep the rest of the ingredients. Chop garlic and parsley, grate parmesan cheese, and squeeze lemon juice.
In a large skillet, melt butter and cook chopped garlic until fragrant but do not brown or burn garlic. Add lemon juice, salt, black pepper and 1/4 cup pasta water to skillet. Bring to a boil and remove from heat.
Optional: If garlic turns blue (it's normal because of its reaction with lemon juice), using a strainer to remove garlic.
Toss pasta in sauce and 1 cup of parmesan cheese. Add additional 1 or 2 tbsp pasta water if needed, but note that this is not a wet pasta dish. Garnish with more parmesan cheese and parsley.
Serve and enjoy!