Remove the basil leaves off the stems and measure out about 4 cups. Press down on the leaves to ensure they are tightly packed. This will be about 100 grams in weight.
Mince the garlic and squeeze the lemon to get about 2 tbsp of juice.
Place the sunflower seeds in a food processor and process for a couple of minutes, stopping to scrape down the sides. The seeds should mostly be broken down into a paste like consistency.
Add the remaining ingredients (except the oil) and pulse for another minute or so until the basil is processed. You may have to scrape down the sides again a few times.
With the processor running, slowly add the oil through the hole at the top until the oil has been incorporated.
Taste and adjust seasonings (e.g. a little more salt or lemon juice).
Remove the pesto and place in a glass jar and store in the fridge. The pesto will last up to about a week in the fridge. It will turn darker the longer it is exposed to the air.
This recipe make about 1 cup of pesto.