Preheat your oven to 350°F (175°C). Line the bottom of a 9-inch springform pan with parchment paper. In a bowl, whisk together cake flour, baking powder, baking soda, and salt. Gradually stir in granulated sugar, milk, oil, egg, and vanilla extract until smooth, then pour the batter into the prepared pan.

Place the springform pan in the preheated oven and bake for 15 minutes, or until lightly golden and a toothpick inserted comes out clean. Allow to cool completely on a wire rack.

Bloom gelatin in cold water for 5 minutes. Puree mango chunks in a blender, setting some mango puree aside for later. Gently heat bloomed gelatin until melted, then combine with mango puree. In another bowl, whip cream with powdered sugar until soft peaks form, then fold the mango mixture into the whipped cream. Pour over the cooled cake layer and chill in the fridge for at least 4 hours.

For the mango curd, heat the reserved mango puree and sugar in a saucepan until warm. Mix cornstarch with water to create a slurry and stir into the warming mixture. Cook over medium heat, stirring until thickened, about 5-7 minutes. Remove from heat, stir in butter, and strain through a sieve. Cool to room temperature.

Once the mousse is set, pour the cooled mango curd over it, spreading evenly. Cover and chill in the fridge for an additional 12 hours to set completely. Remove from the springform pan, garnish with fresh mango chunks and mint leaves if desired, and slice.