Wash the basil leaves and dry them carefully with a cloth. Place a full spoonful of pine nuts in the mortar and pestle until you obtain a paste. Then add a pinch of coarse salt (don't overdo it, just the tip of a teaspoon) which will be used to crush the basil leaves and the clove of garlic which you will have cut into thin slices and removed the core (if you find basil with small leaves it is the best for the pesto). After crushing for a few minutes, add the extra virgin olive oil and another handful of pine nuts which will remain coarse. Once the consistency is obtained, add the parmesan and pecorino in equal percentages. Mix well and taste. If necessary add more cheese and salt. Nb.: the amount of garlic depends on your tastes.