In a large saucepan, combine the orange gelatin and vanilla pudding mix. Pour in hot water and stir continuously. Heat over medium until boiling for 5 minutes until clear.

Remove from heat and cool slightly. Then, cover and refrigerate for at least 4 hours or overnight until firm.

Once set, gently mix in the Cool Whip until fully integrated without overmixing.

Drain mandarin oranges and fold gently into the mixture using a spatula for even distribution.

Transfer to serving dish, smooth the top, cover, and chill for an additional hour before serving.

Serve chilled and garnish with additional mandarin oranges or a dollop of Cool Whip if desired.