Toast the walnuts: Toast your walnuts in a dry skillet over 4 to 5 minutes and stir them occasionally. You can also toast them on a baking tray in a medium oven for about 8 minutes. Cool completely before using them.
Blend the walnuts: Once cooled, pop the walnuts and garlic cloves into your food processor or blender. Blitz them for a few seconds until roughly chopped.
Blend the pesto: Add in the basil leaves, garlic cloves, parmesan cheese and some salt. Pulse until everything is chopped up.
Add in the oil: Add a little of the oil at a time and blend until you have the consistency you like. Taste and season as you go.