Preheat your oven to 350°F (175°C) and line a 9-inch springform pan with parchment paper. In a mixing bowl, combine your dry ingredients, including cake flour, baking powder, baking soda, and salt. In a separate bowl, whisk together the wet ingredients: sugar, milk, oil, egg, and vanilla extract. Gently mix the wet mixture into the dry ingredients until just combined to form a smooth batter, then pour it into the prepared pan.

Place the filled springform pan in your preheated oven and bake for approximately 15 minutes, or until the cake turns lightly golden and a toothpick inserted in the center comes out clean. Once baked, remove from the oven and let the cake cool completely on a wire rack.

While the cake cools, prepare the mango mousse. In a small bowl, bloom the gelatin powder in cold water for about 5 minutes until it absorbs the moisture. In a blender, process mango chunks until smooth. Separate this puree into two portions, one for the mousse and one for the curd. Melt the bloomed gelatin in the microwave until dissolved, then mix it with the mango puree before folding in cold whipped cream until well incorporated.

Once the cake has cooled completely, pour the mango mousse over the top of the cake layer in the springform pan, smoothing the top with a spatula. Place the assembled cake into the refrigerator and allow it to chill for at least 4 hours, or until the mousse has set firmly.

While the mousse is setting, prepare the mango curd. In a saucepan, heat the reserved mango puree with granulated sugar. In a small bowl, mix cornstarch with water to create a slurry. When the mango mixture is hot but not boiling, stir in the cornstarch slurry and cook over medium heat until it thickens, approximately 5 minutes. Remove from the heat and whisk in unsalted butter until smooth. Let this curd cool to room temperature.

After the mousse has set, pour the cooled mango curd evenly over the top of the mousse layer. Return the Mango Mousse Cake to the refrigerator and chill for an additional 8 hours, or overnight for the best results.