In large bowl combine 2 cups cake mix, butter and egg at low speed. Mix well be thick. Stir in remaining cake mix.Press in bottom and 2 1/2 inch up sides of greased spring form pan. Bake at 350 degrees for 10 to 20 minutes or until sides and center are slightly puffed. Cool.
Combine gelatin and water. Let stand until gelatin is completely dissolved.