Cook sweetened condensed milk and chocolate morsels in a heavy saucepan over medium heat, stirring often, until chocolate morsels melt.
Remove from heat, and stir in rum. Pour into a lightly greased 8-inch square pan. Cover and chill 3 hours or until firm.
Shape mixture into 1 1/4-inch balls; roll in chocolate cookie crumbs and then in powdered sugar. Place balls in miniature paper baking cups, if desired. Store in an airtight container in the refrigerator up to 1 week.