Cook butter and corn syrup in small saucepan on low heat until butter is melted. Add sugar and dry jelly powder; cook and stir 2 min. until jelly powder is completely dissolved. Bring to boil on medium heat; simmer on low heat 5 min., stirring occasionally. Pour immediately over popcorn mixture; mix lightly. Use 2 forks to evenly spread popcorn mixture onto bottom of prepared pan.