Spread 1/2 cup chopped peanuts into a 9-inch circle on a lightly greased baking sheet.
Coat top 2 inches of a 2 1/2-quart glass bowl with butter; place remaining butter in bowl. Add sugar and 1/4 cup water. (Do not stir.) Microwave at HIGH 8 minutes or just until mixture begins to turn light brown; pour over peanuts on baking sheet.
Sprinkle with chocolate morsels; let stand 1 minute. Spread melted morsels evenly over peanut mixture, and sprinkle with remaining 1/4 cup chopped peanuts. Chill until firm. Break into bite-size pieces. Store in an airtight container.