Pesto alla Genovese in a Mortar, With the Trofie, Potatoes and Green Beans It Was Made For

For the pasta:

• 400 g trofie, or trenette or linguine
• 2 medium waxy potatoes, peeled and cut into 1 cm dice
• 150 g fine green beans, topped and cut in half

Method

1. Put the garlic and salt in the mortar and pound to a paste. The salt is the abrasive and it is what breaks the garlic down.
2. Add the pine nuts and pound until they form a creamy paste with the garlic.
3. Add the basil a handful at a time. Do not pound it: press and turn the pestle against the side of the mortar in a rotating motion, crushing the leaves against the stone. This is the step that takes time. Continue until the leaves have become a bright green paste and the mortar is releasing a strong perfume.
4. Add the cheeses and work them in with the pestle.
5. Add the oil in a thin stream, stirring with the pestle or a wooden spoon, until the sauce is loose enough to coat pasta but still holds together. Taste for salt. It should be intensely green and taste of basil first, cheese second, garlic a distant third.
6. Bring a large pan of well-salted water to the boil. Add the potatoes. After five minutes add the pasta. Two minutes before the pasta is done, add the beans. Everything should finish together, the potatoes just yielding, the beans still bright.
7. Reserve a cup of the cooking water and drain. Put the pesto in a warm serving bowl, loosen it with two or three tablespoons of the cooking water, add the pasta, potatoes and beans and toss until every piece is coated. Serve at once, with more cheese if wanted.

Notes

Pesto is never cooked and never heated directly. It goes onto hot pasta in a bowl, off the heat, and the pasta's warmth is all it needs. Put it in a pan and it splits and goes brown.

The potatoes and beans are not a modern healthy addition; they are the Ligurian way of serving trofie al pesto and have been for as long as anyone has written the dish down. The potato starch thickens the sauce and the beans give it something to be sharp against. Trofie themselves, the short twisted hand-rolled shapes traditional around Sori east of Genoa, are made for catching a sauce of this texture; linguine or trenette are the flat alternatives and are equally traditional in the city.

To keep pesto for a few days, press it into a jar, cover the surface completely with a layer of oil so no air touches it, and refrigerate. It freezes well without the cheese, which is stirred in after thawing. It goes brown on contact with air and there is no trick to prevent it other than eating it. For a sauce from the other end of the Mediterranean that lives by the same rule, pounded not blended and eaten fresh, see our toum recipe, and for a different herb sauce made the same way, our chermoula.