BLENDER PESTO WITH PENNE

2 cups fresh basil leaves
1/2 cup olive oil
2 tablespoons walnuts or pine nuts
2 cloves peeled garlic, lightly crushed with a heavy knife
1 teaspoon salt
1/2 cup freshly grated Parmesan cheese
3 tablespoons butter, room temperature
3/4 pound cooked penne (some cooking water reserved)

Put basil, olive oil, nuts, garlic and salt in a blender (or food processor) and mix at high speed. Stop from time to time to scrape down sides with a rubber spatula. When ingredients are blended, pour them into a bowl and beat in the cheese. When the cheese has been evenly incorporated into the other ingredients, beat in the butter.

Before spooning pesto over cooked penne, add a tablespoon or two of the hot water in which the pasta has boiled.

TO FREEZE AHEAD:
If freezing this pesto, blend the basil, olive oil, nuts, garlic and salt in a blender and freeze. To use, thaw the pesto mixture and then add the cheese and butter.

Makes 4 servings
Adapted from source: The Classic Italian Cook Book by Marcella Hazan