In a saucepan, heat the mango puree and sugar over low heat until sugar is dissolved.
In a small bowl, sprinkle gelatin over 1/4 cup of cold water. Let it bloom for 5 minutes.
Add bloomed gelatin to the warm mango mixture and stir until completely dissolved. Let it cool to room temperature.
In a separate bowl, whip the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
Gently fold the whipped cream into the mango mixture until well combined.
Slice the pre-made sponge cake into two layers. Place one layer at the bottom of a springform pan.
Pour the mango mousse mixture over the cake layer. Place the second cake layer on top.
Refrigerate the cake for at least 4 hours or until set.
Before serving, garnish with fresh mango slices.
Slice and enjoy your Mango Mousse Cake!