Toast the walnuts (or other nuts) until they are warm and fragrant. Do not burn. Add to a cold bowl and set aside.
Remove mint leaves from the stems. Wash and spin in the salad spinner to remove excess water.
Chop parsley leaves off the bunch, then repeat in the salad spinner to remove excess water.
Add the herbs to the blender, along with the garlic, toasted nuts, and a little kosher salt and freshly ground pepper. Add the lid to the blender with the center part removed.
Measure out 3/4 cup of the extra virgin olive oil. Slowly pour into the running blender through the open top until the cup is empty. If the contents don't seem to be chopping and mixing, turn OFF the mixer and use a spatula to move things around in the bottom. Remove the spatula, replace the lid, and try again. Add more olive oil a little at a time until the blender moves and you get the right consistency.
Pour the pesto into a bowl, and add the Parmesan cheese. Stir until completely blended. Add to a storage container and either refrigerate for a week or freeze for later. Makes about 3 to 4 cups of pesto.