Add half of the pineapple and half of the milk to a food processor. Puree until smooth.
Add in remaining pineapple and puree.
Add in remaining milk, a few tablespoons at a time, and puree. You want to reach a consistency of froyo that has sat out for about an hour. So you might use more milk.
Once you reach that consistency, transfer the contents to a bowl, cover and place in the freezer for 30 minutes to an hour, to firm up.