How to Make It
Preheat the oven to 350°. Spread the walnuts on a rimmed baking sheet and toast for 12 minutes, or until golden. Cool the walnuts and finely chop.
In a mortar, mash the garlic with a pinch each of crushed red pepper and salt until a paste forms. Add the walnuts and parsley and pound to a coarse paste. Slowly add the olive oil, pounding and stirring until blended. Stir in the Parmesan and season with salt.
If you don't have a mortar, make the pesto in a food processor, quickly pulsing the ingredients.