2 cups fresh basil leaves, tightly packed
1⁄2 cup olive oil
3 tablespoons pine nuts or toasted pumpkin seeds
2 garlic cloves, minced
1-2 teaspoons salt
1⁄2 cup Parmesan Reggiano cheese, freshly grated
3 tablespoons butter, softened to room temperature (optional)
*Freezing pesto: Make pesto through to the end of Step 1, cover with a thin layer of olive oil and freeze it without cheese and butter in it. Add the cheese and butter when it is thawed, just before serving.