Preheat oven to 400 degrees F (200 degrees C). Wash beets, and place in a roasting pan. Bake for 45 minutes to 1 hour, or until tender. Set aside to cool.
Melt butter in a large skillet over medium heat. Stir in onion, pears, sugar, and vinegar; cook, stirring frequently, for 20 minutes.
When the beets are cool enough to handle, peel and coarsely chop.
Puree onion mixture in a food processor with metal blade. Add salt and 1/2 of the beets; pulse 4 to 5 times. Add remaining beets, and pulse 2 to 3 times.
