Preheat oven to 350 F. Grease the bottom of two 9 inch round cake pans and line their bases with parchment paper.
In the bowl of a stand mixer (or use a hand-held mixer), beat the eggs on high speed until light and frothy. Add sugar gradually while the mixer is still running. Continue beating until the mixture is thick and has tripled in volume. When you lift the beaters the mixture should fall back in ribbons that stay in the surface for about 10 seconds.
Sift the flour, baking powder and cornstarch together in a bowl. Gradually fold the powders to the eggs using a rubber spatula, just until no streaks of flour remain. Lastly, gently fold in the melted butter.
Pour and scrape the batter equally between 2 cake pans. Bake at 350 F for about 25 minutes, or until the cake springs to the touch. Let cool on a wire rack and peel off the parchment paper backing.
Mix together sugar and cornstarch in a medium saucepan. In another bowl, stir together the mango puree, sour cream and condensed milk. Stir the wet mixture to the cornstarch mixture in the pan until smooth.
Beat the egg yolks briefly. Add approximately 1 cup of the hot mixture into the yolks. Stir quickly and put everything back to the hot pan. Set pan over medium heat. Cook for 3-5 minutes more, stirring constantly until the mixture is really thick. Let the filling cool down a bit. Meanwhile, whip the heavy cream until thick and fluffy.
Lay one cake on a serving plate or cake board. Spread about 1/2 of the mango cream, starting by scooping the cream into the center and spreading it outwards, leaving about half an inch border on the edges. This is to prevent the cream from oozing out when you top it with the second layer.
Lay the second layer on top of the mango cream. Pipe whipped cream using a star tip around the edges of the circle. Spread the remaining cream inside the whipped cream borders and smoothen it with an angled spatula.