Pesto

Method

1. toast3 min
   dry pan, medium-low
   pine nuts, shaking constantly until straw-coloured, then tip them onto a cold plate — they carry enough residual heat to scorch in the pan, and burnt pine nut is bitter in a way no amount of cheese hides. Cool completely before they meet the basil.
2. mince2 min
   processor bowl, or mortar
   garlic + salt + cooled pine nuts, worked to a rough paste. The coarse salt is the abrasive here: it shreds the garlic and the nuts into something that will hold oil, and doing this first means the basil needs only seconds of blade time later.
3. mix2 min
   short pulses, no more than 10
   + basil leaves, pulsed in bursts and scraped down once. Bruised basil leaks polyphenol oxidase, which browns and turns bitter on contact with air and heat — brief pulses cut the leaves, sustained blending grinds them and gives you dull olive sludge.
4. emulsify3 min
   motor off between additions, or stirred by hand
   + olive oil in a thin stream, pulsing just to combine. Extra virgin oil is fragile under high shear: over-processing ruptures the fruit cells and releases a metallic bitterness, so finish the oil by hand with a spoon if the paste is already loose.
5. fold2 min
   machine off, room temperature
   + parmesan (+ pecorino, lemon juice, pepper), stirred in by hand = pesto. Cheese never goes in with the blade running — friction heat melts its butterfat out of suspension and the sauce turns from creamy to grainy and greasy, and it cannot be brought back.
6. store1 min
   jar, oil-sealed, refrigerated
   press flat in a jar and pour a film of oil over the surface. Pesto browns from the top down by oxidation, not spoilage, so excluding air keeps it green for three days; freeze it before adding the cheese if you want longer.