Toast the nuts in a small, heavy skillet over medium heat, stirring frequently, until just golden and fragrant, 4 to 5 minutes. Transfer the nuts to a plate.

Add the garlic to the empty skillet. Toast, shaking the pan occasionally, until fragrant and the color of the cloves deepens slightly, about 7 minutes. Let the garlic cool, then peel and chop.

Combine the basil and parsley (if using) in a heavy-duty gallon-size zipper-lock plastic bag. Pound the bag with the flat side of a meat pounder or rolling pin until all the leaves are bruised.

Place the nuts, garlic, pounded herbs, oil, and ¼ tsp. salt in a food processor. Process until smooth, stopping as necessary to scrape down the sides of the workbowl. Transfer the mixture to a small bowl, stir in parmesan, and adjust the salt to taste. The surface of the pesto can be covered with a sheet of plastic wrap or a thin film of oil and refrigerate for up to 3 days.