In a mixing bowl, combine the Jello powder with 1 cup of boiling water and stir until completely dissolved.

Add 1 cup of cold water to the dissolved Jello and stir to combine.

Refrigerate the mixture for 30 minutes or until slightly thickened.

In another bowl, whip 1 cup of heavy whipping cream with an electric mixer or whisk until soft peaks form.

If desired, gradually add 1/4 cup of powdered sugar while whipping to sweeten the cream.

Gently fold the chilled Jello mixture into the whipped cream using a rubber spatula until fully combined.

Spoon the mousse into serving cups or bowls.

Refrigerate for at least 1 hour or until set before serving.