In a pestle and mortar, add a pinch of salt and the garlic clove. Pound and grind until this forms a paste.
Add the pine nuts and again, pound and grind until you have a paste.
Next, start adding the basil leaves in – a handful at a time, not all at once – and in a grinding motion, not pounding, slowly break the basil leaves down. Keep adding basil and grinding in this way until you have used all of it.
Add the Parmigiano and incorporate, followed by the Pecorino.
Add the olive oil in a few batches, incorporating after each addition.