Drizzle some olive oil in a large pot of boiling salted water, add the capellini, and cook al dente.
Meanwhile, melt the butter in a large saute pan. Add the zest and juice of 2 lemons, 1 teaspoon salt, and 1 teaspoon pepper and bring to a simmer. When the pasta is cooked, use tongs to remove it from the pot and place it in the saute pan. Toss the capellini with the butter mixture. If the capellini is dry, add extra pasta water.
Place one serving of pasta on each of 6 plates. Garnish with grated zest of 1 lemon and serve immediately.