15 oz cans or jars sliced beets, drained well.
In medium saucepan, combine sugar, cornstarch, salt, vinegar and water, place over medium heat. Stir until smooth.
Bring to a boil, stirring, until thickened. Add beets and onion. Simmer on low 10 mins. Add butter, stir until melted.
Let cool. Pour into a lg jar or bowl. Refrigerate until serving.