Harvest Nettles: Harvest (young) nettles while wearing gloves by cutting stem about 1/4-1/3 of the way down the plant. (Don't harvest the lower leaves.) Remove and discard stems.
Measure Nettles: Weigh 6 oz nettles (about 6 packed cups).
Prepare Ice Bath: Have a large colander in the sink and large bowl of cold water with ice cubes prepped for an ice bath.
Blanch Nettles: Bring a large pot of water to a boil and add 6 oz nettle leaves, using a large spoon to make sure leaves are fully submerged, then start the timer for 45 seconds.
Strain + Dry Nettles: Once timer goes off, strain the water using the colander in the sink, then quickly transfer leaves to the ice bath. Remove the gloves and check to make sure leaves are cooled, then strain water in the colander again. Use your hands to gently squeeze the water out of the leaves, then transfer to a salad spinner. Separate the leaves and spin to get as much moisture out as possible. Then wrap the leaves in a clean kitchen towel and pat dry. (You'll want to remove as much moisture as possible, otherwise the pesto will be watery.)
Pesto: Place ⅓ cup pepitas and 3 cloves garlic in a food processor and process until fine. Scrape the sides with a rubber spatula, then add the blanched, cooled, and patted dry nettle leaves, 2 Tbsp lemon juice, 1 Tbsp nutritional yeast, ½ tsp sea salt. Process until a paste-like consistency, stopping to scrape the sides a couple of times. Remove the lid and the blade and use the spatula to stir in ¼ cup olive oil. Taste, adding anything more it may need.