Bring a large pot of salted water to a boil. Cook your pasta of choice until al dente. Before draining, reserve about 1 cup of the starchy pasta water. Set it aside.
In a large mixing bowl, whisk together the egg yolks, olive oil, grated parmesan, crushed garlic, chopped parsley, lemon juice, and a generous amount of freshly ground black pepper. The mixture will be thick at this point.
Slowly whisk in the reserved hot pasta water, a little at a time, until the sauce becomes creamy and smooth. You may not need the entire cup, stop when you reach your desired consistency.
Add the hot, drained pasta directly to the bowl and toss well until every strand is coated in the glossy, garlicky sauce. The heat from the pasta will help thicken and emulsify the sauce.
Plate immediately with extra parmesan, a drizzle of olive oil, and chili flakes if you like. Serve warm and enjoy!