The type of cherries used to make a clafoutis highly depends on the recipe you find, and family traditions. Some like to use whole fresh cherries, other go for pitted ones. Using un-pitted cherries supposedly create a much stronger fruit flavour and helps to keep the juices in. I have made this recipe with frozen pitted cherries before and found the taste to be quite blend, so I would highly recommend using either fresh cherries or like here, Pitted Morello Cherries. It is a such great Morello Cherries Recipe if you love those types of cherries! They are known for they strong sweet and sour taste that I personally love in clafoutis. The tart flavour of morello cherries simply balances the relatively sweet dessert perfectly. Morello Cherries (known as "Griottes" in French) are easily found in jars in the canned fruit section of your supermarket. They usually come already pitted and are kept in a syrup that I love to use to top the baked dessert.