A recipe from the Sneaky Kitchen
1 1/3 C. pitted prunes (8 oz.)
6 Tbsp. water
Place in a food processor or blender, and pulse on and off until the prunes are completely pureed.
For a thicker prune butter, which can also be used as a spread, use a pound of pitted prunes and 1 cup of very hot water.
Note that prunes are so high in natural sugar, they need no further sweetening.