In a bowl, dissolve Jell-O in boiling water.
Stir in cold water and orange juice.
Chill until slightly thickened (about 45–60 minutes).
Fold in whipped topping and vanilla.
Pour into serving dishes or a trifle bowl.
Chill until fully set (2–3 hours).
Garnish with mandarin oranges or a swirl of whipped cream.
Creamy, citrusy, and perfect for summer!