Remove the stems from the basil leaves, then wash them and dry them well with kitchen paper. Cut the Parmigiano, pecorino and garlic into pieces and put them in a food processor with the pine nuts, walnuts, salt and basil. Chop (1) thoroughly and pour the sauce into a bowl that’s large enough to contain the pasta as well. Add the olive oil, a little at a time, stirring very slowly to amalgamate everything well.
This sauce can be used to dress linguine, tagliatelle and spaghetti, as well as all short pasta shapes, and it’s also delicious on egg pasta (pappardelle, tagliolini, ravioli). It’s important not to strain the pasta too much and to set aside a few spoonfuls of the water it was cooked in, these can then be added to the pasta if it seems too dry and not creamy enough. A spoonful of pesto added to minestrone or creamed vegetable soups makes them special. It’s an excellent “seasoning” that can be added to many pasta sauces (especially tomato based ones) to enhance the flavour.
(1) Nowadays both housewives and professional cooks often rely on food processors or blenders, but real pesto is made using a marble or wood mortar and pestle. Here is exactly how it’s done: you start by “pestare” (= crushing) the basil leaves and garlic. You crush and grind them until the two ingredients are reduced to a pulp. Then you add the pine nuts and salt and continue crushing as you gradually add the olive oil, amalgamating it with the rest of the mixture. The sauce is completed with the cheese (you can add it already grated). The rule is that it should be half pecorino and half Parmigiano, but some just use the former and others adjust the percentages according to their taste.