01 - Dissolve orange gelatin in 2 cups boiling water, stirring until fully dissolved. Add 1 cup cold water and mix thoroughly. Allow to cool for 10 minutes.
02 - Gently fold drained mandarin oranges and crushed pineapple into the cooled gelatin mixture.
03 - Transfer mixture to a 9x13-inch glass dish or decorative serving bowl. Refrigerate for 2 hours or until completely set.
04 - In separate bowl, fold together sour cream, mini marshmallows, and whipped topping until evenly combined.
05 - Spread creamy mixture evenly over set gelatin base.
06 - Refrigerate for at least 1 additional hour before serving. Garnish with mandarin orange segments or orange zest if desired.