From the Julia Child of Italian Cooking, this is Marcella Hazan's recipe for pesto. Its the first I've ever tasted and the only one I'll ever use. I've tried other recipes and nothing surpasses this, especially not any you'll get from a restaurant. Quality ingredients are important in simple recipes like this. The aromas in pesto's ingredients are subtle and its flavor varies depending on the brand and quality of the ingredients you choose. Make sure to find the best olive oil, the freshest basil (if it doesn't smell right or fragrant, don't bother using it, it will be a waste of expensive ingredients.) The cheeses mentioned should be sought and used. Use a high quality butter if possible.