Toast raw pistachios for 2-3 minutes on low heat, until starting to smell a bit toasty and browned, then take them off the heat.
Remove lemon basil leaves from stems, avoiding getting any flowers or seeds into the mixture.
Measure 2 cups of leaves, lightly packed, and then wash them all carefully. Then add all of them to the bowl of your food processor with 1 Tablespoon of oil and blend for 10 seconds, until all the basil leaves have been lightly chopped and coated in oil.
Scrape down the sides, and then add the garlic, pistachios, salt, and 1 Tablespoon of oil to the lemon basil. Put on the lid and pulse the ingredients for 10-20 seconds. Really high-powered food processors may only need 1 more Tablespoon of oil for the rest of the pesto.
Next, slowly add in all the rest of your oil as needed, scraping down the sides at least twice and blend until very smooth (30 seconds to 2 minutes). Once smooth, your pesto is all ready to use!