In a food processor, pulse the pine nuts, walnuts, garlic, parmesan cheese, basil, and a pinch of salt and pepper. Slowly pour in the olive oil while continuing to pulse. Stop once all ingredients are combined and the pesto is smooth.

Cut cleaned string beans into 1 inch pieces.

In a pot of salted boiling water, boil the pasta and string beans about 8-10 minutes (until the pasta is al dente).

Reserve 2 tablespoon pasta water.

Strain pasta and string beans.

In the pot, combine pasta, string beans, pesto and reserved pasta water. Mix to combine.