Preheat the oven to 165°C (325°F). Prepare two 9-inch round cake pans with parchment paper on the bottom only; do not grease the sides to allow the batter to climb.

In a large mixing bowl, whisk the egg yolks, mango puree, vegetable oil, and vanilla extract until the mixture is fully emulsified and smooth.

Sift the cake flour, 1 cup of granulated sugar, baking powder, and salt together, then whisk them into the mango yolk mixture until no lumps remain.

In a separate, completely clean and grease-free bowl, beat the egg whites and cream of tartar on medium speed until soft peaks form.

Gradually add the remaining 0.25 cup of sugar to the egg whites while continuing to beat at high speed until stiff, glossy peaks are achieved.

Gently fold one-third of the meringue into the mango batter using a silicone spatula to lighten the base.

Carefully fold the remaining meringue into the batter in two additions using a gentle figure-eight motion, being careful not to deflate the air bubbles.

Divide the batter evenly between the two pans and tap each pan once firmly on the counter to release any large air pockets.

Bake for 45 to 50 minutes, or until the cake surface springs back when lightly pressed and a wooden skewer comes out clean.

Immediately invert the pans onto a cooling rack and allow the cakes to cool completely within the pans to maintain their height and soft structure.

Once cold, run a thin offset spatula around the edges to release the cakes. Whip the heavy cream and powdered sugar to stiff peaks for the frosting.

Layer the cake by spreading whipped cream and half of the diced mangoes between the sponges, then frost the top and sides with the remaining cream and garnish with fresh mango slices.