Start the recipe by removing the pistachios from their shells. Once they’re shelled, blanch them in boiling water for a minute and a half
Immediately roll the blanched pistachios in a tea towel or rough dish cloth. The husks should remove easily.
Place the basil, garlic, husked pistachios and salt in the mortar. Pound the garlic, basil and salt on the bottom until everything is sufficiently crushed. Crush all the ingredients by spinning the pestle against the side of the mortar until a rough paste forms.
Once you’ve formed the basil/garlic/salt paste, slowly drizzle in the olive oil. Hazan says to add the cheese at this step but, in our view, this isn’t necessary. Continue to add the olive oil in a thin stream. Mix with a wooden spoon in a circular motion until everything is incorporated.
Once the olive oil is incorporated, add the butter. (This is an optional step.)
Once the olive oil and optoinal butter are incorporated, add the two grated cheeses. They should mix in easily with a spoon.
The pesto is now ready. You can store some or all of it for up to a week in a plastic container. It’s important to line the top of the pesto with plastic wrap so that the pesto retains its verdant green color.
