Lemon pesto spaghetti, all zest and no juice

Modeled on the pesto di limone that Giovanna Aceto makes on her family's farm in Amalfi, where the lemons are practically a fruit course. This version earns its keep twice: the pasta cooks in lemon-scented water, then wears a lemon-almond pesto on top. The almonds get toasted first, a small act of house insubordination that gives all that perfume a proper floor.

1. Toast the almonds in a dry 12-inch skillet over medium, tossing often, until golden and fragrant, 3 to 5 minutes. Tip them out to cool.
2. With a vegetable peeler, preferably the Y-shaped sort, strip the zest from the lemons in long, wide ribbons, taking the colored skin and none of the bitter white pith. You want about ⅔ cup of strips. Keep the naked lemons for another job, only the zest works today.
3. In a large pot, bring 2 quarts water, 1½ teaspoons salt, 1 teaspoon of the sugar and half the zest strips to a boil and cook 2 minutes, then fish out and discard the zest. The oils stay behind, so the noodles season themselves from the inside. Add the spaghetti and cook until al dente. Reserve 1½ cups of the cooking water, drain and return the pasta to the pot.
4. Meanwhile, in a food processor, combine the remaining zest strips, the almonds, the garlic, the Parmesan, the remaining ½ teaspoon sugar and ¼ teaspoon each salt and pepper. Process until it looks like coarse sand, 10 to 20 seconds. Add the oil and process just until incorporated, about another 10 seconds. It should stay a little gritty, this is a pesto, not a mayonnaise.
5. Add the pesto and ¾ cup of the reserved pasta water to the pot and toss hard until every strand is coated, adding more water as needed to loosen. Taste and season with salt and pepper. Serve drizzled with more oil, showered with grated Parmesan and the chives if using.