We almost never use a recipe when making pesto. Once you've made it a few times, you get a sense for the proportions that you like. What we have here is a guideline, but feel free to stray from this if you find it too garlicky (or not garlicky enough!), too cheesy (or not cheesy enough!), or too lemony. As with any recipe, it's important to taste as you go and adjust it to your tastes. You can always add more of something later on.