Walnut pesto is a type of sauce in which basil or parsley is blended until it is smooth and creamy. Although cheese can be added to the mixture, it is not necessary. Walnuts — whether toasted or raw, whole or diced — are then added to the sauce. Pesto is a traditional Italian dish that is often served over pasta, on toasted bread or used as a topping for meats. There are many varieties of pesto, some varying by region, but most involve grinding leafy greens down into a paste.
The first mention of pesto comes from Genoa. It originally was a blend of garlic, basil, pine nuts, olive oil and grated cheese. The basic recipe remains mostly the same, but variations in ingredients have emerged that expand the flavors and uses of the pesto. Walnuts have been included in Italian cuisine for some time, so it could be expected that they have made it into this classic dish.
Cooking with walnuts is not especially difficult, except that a decent-quality ingredient should be found. Like most nuts, walnuts contain oils, meaning they can easily go rancid if left on a shelf for a long time. They should be stored in a refrigerator or freezer if they are not going to be used within a few weeks.
Exactly how the walnuts are employed in the dish is a matter of taste. They are sometimes roasted in an oven or browned in a pan to develop their flavor. They also can be mixed into the walnut pesto in raw or diced form to provide texture.
Pesto can be made from basil, as is traditional, or other greens, such as spinach. Parsley and arugula, or any combination thereof, are popular choices. Ingredients such as onions and garlic can be added to taste. The oldest recipes for pesto called for the ingredients to be mashed into a paste using a mortar and pestle. For this reason, the name "pesto" means "paste," though food processors have made mixing the ingredients easier.
The combination of ingredients has good nutritional value. Basil provides vitamins A and K, calcium and potassium. It also contains omega-3 fatty acids. Walnuts contain thiamin, folates and vitamin B6. There also is a large amount of protein in walnuts.
Walnut pesto is usually prepared at room temperature and heated through only once it is placed over hot pasta. There are recipes that call for it to be cooked, such as when used as a coating for pork or other meats. If cooking walnut pesto, it is important to ensure that the walnuts do not burn and the pesto itself does not break as it is heated.