Beat ¾ cup butter and 1-1/3 cups peanut butter in a large bowl until blended.

Gradually add 3 cups powdered sugar, beating until well blended.

Cover; refrigerate until firm enough to shape, about 30 minutes.

Shape into 1-inch balls.

Cover; refrigerate until firm, about 1 hour.

Place 2 cups chocolate chips and 1 tablespoon shortening in a medium microwave-safe bowl.

Microwave at MEDIUM (50%) for 1 minute; stir. If necessary, microwave at MEDIUM an additional 15 seconds at a time, stirring after each heating, just until chips are melted when stirred.

Dip each ball into chocolate mixture, coating ¾ of the ball.

Place on wax paper, uncoated side up. Let stand until chocolate hardens.

Store, covered, in the refrigerator.