Celery Leaf, Parsley and Pistachio Pesto

1 cup packed flat-leaf parsley leaves

1 cup packed celery leaves

2 cloves garlic

¼ to ½ teaspoon sea salt ¼ cup plus 1 tablespoon shelled, unsalted pistachios, toasted and coarsely chopped (see note)

¼ cup extra-virgin olive oil

¼ ounce Parmigiano-Reggiano or Grana Padano cheese, finely grated (optional)

Chop the parsley and the celery leaves. Use a mortar and pestle to pound the garlic with ¼ teaspoon of the salt to form a smooth paste. (Alternately, use the flat side of a chef's knife to crush the garlic, then mince it with the salt until extremely fine.)

Use a large mortar and pestle or a food processor to reduce the pistachios to fine crumbs.

If using a mortar and pestle, add the parsley and celery leaves to the garlic and pistachios a bit at a time, pounding well after each addition, until they break down to a coarse paste, scraping around the bowl occasionally to incorporate. If using a food processor, add the leaves to the pistachios all at once, along with the garlic; pulse until broken down to a coarse paste, about 1 minute, stopping once to scrape down the sides of the bowl.

Add the oil in a slow stream, stirring or pulsing until fully blended. Scrape the pesto into a medium bowl. If serving right away, stir in the cheese, if using. If you're not adding the cheese, taste the pesto and add some or all of the remaining salt, as needed. If you're refrigerating the pesto, cover with plastic wrap pressed directly onto the surface. If you're adding the cheese, do so right before serving.

Note: Toast pistachios on a baking sheet, spread in a single layer, in a 400-degree oven for 4 to 5 minutes, shaking them once so they brown evenly. Cool completely before using.