Basil Pesto

Make it step by step

1. Pick the basil leaves off the stalks and wash them only if they need it.
2. Dry them completely, in a salad spinner or between two tea towels, until no water beads on a leaf. Water thins the sauce and stops the oil holding.
3. Toast the pine nuts in a dry frying pan over medium-low heat for 3-4 minutes, shaking the pan constantly.
4. Stop when they smell nutty and are patched pale gold. They go from pale to burnt inside a minute at the end, and one scorched batch is bitter through the whole jar.
5. Tip them onto a cold plate and cool them completely.
6. Pound the garlic clove with the coarse salt in a mortar until it is a smooth paste. The salt crystals are the abrasive, which is why they go in with the garlic rather than at the end.
7. Add the cooled pine nuts and pound them to a rough paste.
8. Add the basil a small handful at a time, grinding it against the side of the mortar in a circular motion rather than hammering straight down.
9. Grind rather than chop or hammer. Bruised basil oxidises and blackens at the cut edges within minutes, and the sauce goes from bright green to army green while you are still making it.
10. Work in the grated parmesan and pecorino.
11. Stir the olive oil in by hand at the end rather than pounding it in.
12. If you use a food processor instead, chill the bowl and the blade, pulse in short bursts, keep the oil out until the very end and stop while it is still coarse. A machine run continuously heats the paste through friction, which is the fastest route to a dark, bitter pesto.
13. Taste it. It should be assertive on its own, since it will be spread thin across pasta or stirred into a pan of soup.
14. Never cook it. Stir it into hot pasta off the heat, loosened with a ladle of the starchy cooking water that the cacio e pepe in this collection explains, or into a bowl of the minestrone at the table. Boiled, it goes khaki and the raw garlic turns harsh.
15. Scrape it into a small jar and level the top.
16. Pour a film of olive oil over the surface, which keeps the air off and holds the colour.
17. Keep the jar in the fridge and use it within four days.
18. Keep it in the fridge and never in a cupboard, oil film or no oil film. Oil is not a preservative: raw garlic held under oil at room temperature is exactly the airless, low-acid condition Clostridium botulinum needs, and a jar of pesto is not an acidified preserve.
19. Freeze whatever will not be used within the week in an ice-cube tray, for up to three months.