Pesto is, on the surface, a very simple sauce. It requires no cooking, and has few ingredients. And yet read just any authoritative source on pesto and despite its simplicity, there are several variables to explore when making pesto. Read those who wax poetic on proper pesto, and you’ll usually encounter the following rules:
Ingredients: 5 to 6 ounces (2 healthy bunches or about 6 cups gently packed) basil leaves, or any other green. 1/2 cup pine nuts, or any other nut. 1/2 cup grated Parmesan cheese, or any other hard cheese. 1 to 2 garlic cloves. 1/4 teaspoon salt. 1/4 to 1/2 cup extra-virgin olive oil.
Blend half the basil with the nuts, cheese, and garlic: Combine half of the basil with the nuts, cheese, cloves, and salt in a blender or food processor. Blend continuously until the ingredients are finely chopped.
Blend in the rest of the basil: Scrape down the sides of the bowl and add the rest of the basil. Blend until a uniform paste has formed. Scrape down the sides of the bowl as needed.
Stream in the olive oil: With the blender running, stream in the olive oil. Less olive oil will make a paste good for spreading on sandwiches and pizzas; more will make a sauce better for pastas and stirring into soup. Scrape down the sides of the bowl and continue blending as needed until the olive oil is emulsified into the basil and the pesto looks uniform.
Taste and adjust: Taste the pesto and add more salt, garlic, nuts, or cheese as needed to taste.
Store your pesto: Pesto will darken and brown very quickly, but will still be tasty and fresh for several days. For best appearance, use it right away. If storing, store it in the smallest container possible and thoroughly press the pesto to eliminate air pockets. Pour a little olive oil over the surface, cover, and refrigerate for up to a week. Pesto can also be frozen for several months.