Peel, core and slice pears. Place pears and water in nonaluminum, heavy-bottom Dutch oven. Simmer, covered, 15 minutes, until tender. Mash with potato masher or whirl in food processor for smoother butter.
Stir in sugar. Cook, uncovered, at bare simmer 1 hour. Stir occasionally. Stir often during the last 30 minutes. Mixture will be very thick.
Spoon into sterilized canning jars; process according to manufacturers instructions. If not processed, refrigerate up to 2 months. Makes 2-2/3 cups.
