Place half of peaches into container of an electric blender; process until coarsely chopped. Pour into a flat-bottomed kettle. Repeat procedure with remaining peaches. Stir in sugar.
Cook over medium-low heat, stirring frequently, 30 minutes or until mixture thickens.
Quickly ladle butter into hot sterilized jars, leaving 1/4-inch headspace. Cover at once with metal lids, and screw bands tight. Process in boiling-water bath 5 minutes.