Al pil-pil, pronounced al-peel-peel, is a sauce originating in the Basque country. The sauce is made from oil along with garlic and guindillas--very small, hot peppers. The two most common dishes using this sauce are bacalao al pil-pil (salted cod) and gambas al pil-pil (shrimp).
When preparing the bacalao, the garlic and peppers are first cooked in the oil and then removed before proceeding. The salted cod (that has been rehydrated and the salt removed) is then cooked in the garlic and pepper-flavored oil, and the garlic and peppers returned to the pan along with additional oil.
The fish and oil mixture is cooked until the sauce has emulsified.
For the gambas recipe, the garlic and peppers are cooked in the oil, and then the shrimp are added, similar to gambas al ajillo (garlic shrimp).
Whether codfish or shrimp, the al pil-pil recipe is usually served in individual clay dishes.