Classic Basil Pesto

From Epicurious.  I just used one pack of fresh basil from the store, and then made a half recipe.

4 cups fresh basil leaves (from about 3 large bunches)

1/2 cup olive oil

1/3 cup pine nuts

2 garlic cloves

1/4 cup freshly grated Parmesan cheese

1/4 cup freshly grated pecorino Sardo or Parmesan cheese

1 teaspoon coarse kosher salt

Combine first 4 ingredients in blender. Blend until paste forms, stopping often to push down basil. Add both cheeses and salt; blend until smooth. Transfer to small bowl. (Can be made 1 day ahead. Top with 1/2 inch olive oil and chill.)