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1
Place basil leaves, pine nuts, garlic, and sea salt into a large mortar.
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2
Using a pestle, gently pound and crush ingredients together in a circular grinding motion until basil is bruised and oils begin to release (3 minutes); do not pulverize (use a food processor only as a last resort, as it damages basil's structure).
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3
Transfer mixture to a glass bowl; add grated Parmigiano Reggiano and Fiore Sardo if using, stirring gently with a wooden spoon.
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4
Slowly drizzle extra virgin olive oil into the bowl while stirring gently with a wooden spoon in one direction only, emulsifying the pesto (2 minutes).
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5
Taste and adjust salt and pepper; pesto should be vibrant green, with visible basil leaves and a fresh, bright aroma.
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6
Store in a glass jar with a thin layer of olive oil on top to prevent oxidation; refrigerate and use within 5 days, or freeze in ice cube trays for up to 3 months.