Pesto (or sub store-bought): In a small food processor or blender, add 2 cups packed fresh basil leaves, ⅓ cup parmesan cheese, ⅓ cup extra virgin olive oil, ¼ cup pine nuts, 2 garlic cloves, 1 teaspoon lemon juice, and ½ teaspoon kosher salt. Blend until smooth. Taste and add additional salt, as desired. Add additional olive oil, a tablespoon at a time, to thin.
Pasta + Pasta Water: Bring a large pot of water to a boil. Cook ½ pound medium shells pasta al dente according to package instructions. Remove approx. 1/2 cup pasta water and then drain pasta. Return to warm pot along with the pesto and a splash of paster water (set remaining pasta water aside).
Sauce it up: Stir and let the hot pasta water create a beautiful, thinned out pesto sauce that will coat your noodles beautifully! Add additional splashes of pasta water, as needed, to reach your desired consistency (you may not use it all).
Serve: Serve with some grated or shaved parmesan cheese for garnish.