Castelvetrano olives come from Valle del Belice, a region of Southwestern Sicily. These are medium sized green olives with a crunchy texture and a rich buttery taste. Make sure to purchase these olives from a reliable supplier to make sure they don't dye them. If the olives appear "nuclear green" avoid them! Castelvetrano olives are typically used for making olive oil but they've become popular recently as a table olive. You can buy them with or without pits (with pits have the best flavor) and they are typically packed in water. A reliable supplier is The DeLallo Company.
Of course these are one of the best table olives with the unique blend of crunchy texture and yet they still have that buttery flavor. Once you taste these you may never go back to a plain green olive. Add the pitted olives to a fresh green salad with feta cheese, red onions and sturdy greens like romaine. Or, roast chicken thighs or legs with a lemon and butter sauce with the olives.
Look for these olives in a good deli or a store that specializes in Italian foods. You may find them at Trader Joe's or Whole Foods Market too. You can always purchase them online at Amazon.com: Whole Castelvetrano Olives.
If you don't have Castelvetrano olives then you can substitute: