Everything I know about pesto I learned from Fred Plotkin in his book Recipes from Paradise (Little, Brown and Company, 1997). If you are even remotely interested in Liguria and her food (or for that matter, Italy and her food) I strongly urge you to get a copy of this book. Mr. Plotkin writes with verve and a very definite point of view. The recipes are excellent and accurate, but even better, the book is just plain fun to read.
Here is his recipe for Classic Pesto from the book which I quote in its entirety:
1 pinch coarse sea salt
60 small or 30 large fresh basil leaves, carefully wiped, stems and spines removed*
2 cloves of garlic, peeled, with the green heart removed
3 tablespoons/22 g pinoli
2 tablespoons/15 g fresh, finely grated Pecorino Romano
2 tablespoons/15 g fresh, finely grated Parmigiano-Reggiano
3 to 4 tablespoons/45 to 60 ml Ligurian extravirgin olive oil
makes about 1 cup/225 ml
Add the sea salt and a few of the basil leaves to your marble mortar. Using a wooden pestle, crush the leaves and salt gently but with a firm rhythm against the bottom and sides of the mortar so that the leaves gradually come apart. Keep adding leaves a few at a time until they are all used. While the leaves are still partly intact, add the garlic and then pound it too, just until it is mashed and has released its juice. Then add the pinoli and pound them until they are reduced to paste. Stir the pestle in the mortar so that the ingredients combine. Then add the Pecorino Romano and Parmigiano-Reggiano and stir again to combine the ingredients. Now add the olive oil a little at a time, stirring with the pestle to make a sauce of a creamy consistency. Some people like more oil, some less, so the amount I recommend is a guideline. Your goal is to have a thick creamy sauce. If you choose not to use all of the oil, that is fine. The result should be fully amalgamated and of a medium bright green color.
If you want to know any of the other 15 pesto recipes in Mr. Plotkin’s book, or the secret of adding a couple of tablespoons of the pasta water to the sauce, why you’ll just have to get your hands on a copy of the book.
* Mr. Plotkin advocates wiping leaves clean rather than washing them. Washing them damages their oil; wiping enhances their perfume. Also, he prefers small leaves to large, as they are more flavorful and less minty.