Add 2 tablespoons of salt to a large pot of boiling water. Add the capellini and cook for 3 to 4 minutes, until just al dente.
Meanwhile, heat a large (12-inch) saute pan, add the butter, and heat until the butter is melted. Add the zest and juice of the 2 lemons. Add 2 teaspoons salt and 1 teaspoon pepper and swirl the pan to combine.
As soon as the pasta is cooked, lift the pasta out of the water with tongs, allowing most but not all of the water to drain back into the pot, and add all the pasta to the sauce. Cook for one minute, adding pasta water to the sauce with a ladle just enough to keep the pasta moist.
Transfer the pasta to a serving platter or individual plates. Garnish with more lemon zest, sprinkle with salt and pepper, and squeeze a little lemon juice on top. Serve hot.