Preheat oven to 325 degrees F. Spread shelled pistachios in an even layer on a cookie sheet. Bake for 5 to 10 minutes or until fragrant but not yet browned. Remove from oven and let cool slightly.

Transfer toasted pistachios to the bowl of a food processor or blender. Process until pistachios break down into a fine powder.

Continue to process the nuts for 5 to 10 minutes, scraping down the sides of the bowl as you go, until smooth and creamy. If desired, add a teaspoon of pistachio oil to help the butter process more smoothly.

Once the butter has achieved your desired consistency, add a pinch of salt if desired and pulse once or twice more to combine.

Transfer to a jar or other container with an airtight lid. Store refrigerated for up to one month or freeze for longer storage.