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1
Place the coarse salt and garlic in a marble mortar. Work the pestle in a circular motion — not straight down — until the garlic is fully reduced to a smooth, even paste. The paste is ready when no fibrous strands remain and the surface is uniformly glossy.
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2
Add the basil leaves in two or three stages. After each addition, work in a continuous circular motion, pressing the leaves against the mortar wall rather than pounding them vertically. If working without chilled conditions, set the mortar over a bowl of ice. Continue until the basil is reduced to a creamy, intensely green mass. The stage is complete when the colour is vivid and uniform — no dark or oxidised patches.
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3
Add the pine nuts to the mortar. Continue the circular pestle motion until the nuts are fully incorporated and the paste is cohesive and emulsified. The paste should hold together as a single mass when pressed with the pestle.
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4
Add the grated Pecorino Sardo and Parmigiano Reggiano, maintaining the 1:3 ratio. Fold them into the paste with the pestle using short circular strokes until no dry cheese remains visible and the paste is uniform in texture.
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5
Transfer the paste to a bowl. Add the Ligurian extra-virgin olive oil by spoon in a thin stream, stirring steadily with the spoon — never returning the pestle — until the oil is fully bound into a loose, cohesive sauce. The sauce is ready when it moves as a single body and the green colour remains vivid throughout.
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6
Do not heat the pesto. To serve with pasta, reserve a ladleful of pasta cooking water, drain the pasta off heat, add the pesto cold, and toss, loosening with pasta water by the spoonful. The heat of the pasta alone melds the sauce. The dish is ready when each strand is evenly coated and the pesto retains its bright green colour.