Pistou sauce, or just pistou, is a cold sauce made from cloves of garlic, fresh basil, and olive oil. Some versions also include grated parmesan. Traditionally, the ingredients are crushed and mixed together in a mortar with a pestle, (pistou means pounded in the Provençal language).http://www.foodandwine.com/articles/frances-best-pistou FoodandWine.com.