Roughly chop pears and place in a saucepan with water and apple cider. Bring to a boil then reduce heat and simmer until pears have broken down, about 5 -7 minutes.
Place in blender (or use a stick blender) and process to smooth.
Combine pear purée and sugar (add more sugar if desired) and place sweetened pulp in a medium saucepan. Cook over medium-low heat, stirring frequently, for 1-2 hours or until thick enough so the butter doesn't run off a spoon when turned upside down.