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1
Wipe the herbs and spinach clean with a dry towel; if they are not organic, wipe them with a lightly dampened towel.
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2
Put the sea salt in a large mortar.
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3
Add a few basil leaves, torn into fragments, and 1 garlic clove.
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4
Start grinding with the pestle in a circular motion until everything is reduced to a fine texture.
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5
Add a few more basil leaves and the spinach and grind and gently pound to the same fine consistency.
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6
Continue pounding the basil and herbs, adding the second garlic clove halfway through, until all the leaves are ground to a fine-textured pesto; keep scraping the pesto down into the bottom of the mortar as you work.
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7
With the pestle, gradually stir in the 1/3 cup Parmesan and 3 tablespoons Pecorino cheese; you will have a very dense mixture.
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8
Scrape the pesto off the pestle and down from the sides of the mortar.
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9
Add the olive oil in a thin steady stream, stirring it in with the pestle in a circular motion until fully incorporated.
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10
One-half cup of olive oil makes a very loose pesto; you may want to use less for a thicker pesto.
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11
Cook the spaghetti in a large pot of boiling salted water until al dente.
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12
Drain the pasta, reserving 1/4 cup of the cooking water.
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13
Transfer the pasta to a large bowl and toss with the pesto and 2 tablespoons of the pasta cooking water; add more water if necessary.
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14
Serve immediately, passing additional cheese at the table.
