Preheat your oven to 350° F (175° C) and line the bottom of your pans with parchment paper. Do not grease the sides to allow the cake batter to "crawl" up the sides, helping it rise properly.
Dry ingredients: In a bowl, combine the flour, baking powder, and salt. Whisk together and set aside.
Wet ingredients: In a large bowl, combine the egg yolks, mango purée, ½ cup granulated sugar, oil, lemon zest, and vanilla extract. Whisk until well-combined. Set aside.
Sift half the dry ingredients into the wet, gently folding with a whisk or spatula until just combined. Add the remaining dry ingredients, continuing to fold until smooth. Keep the batter light and fluffy and do not overmix. Set aside.
In a bowl, make the meringue by combining the egg whites, ½ cup granulated sugar, and cream of tartar. Beat at medium-high until firm, glossy peaks form in 7-8 minutes, which stand straight when the whisk is inverted.
Fold ⅓ of the meringue into the wet ingredients to lighten the mixture. Then, gently fold in the rest until just combined and no white streaks are visible. Do not overmix.
Pour the batter into prepared pans and smooth the top. Tap the pans on the counter a few times and run a small knife or a skewer through the batter to release any remaining bubbles or air pockets.
Bake for 25-28 minutes or until a toothpick comes out clean and the cake springs back when touched.
After baking, drop the pans from 6 inches high onto a surface to set the cake's structure and reduce shrinking. Cool completely in the pans, preferably on a wire rack. When fully cooled, run a knife or offset spatula along the edges of the pan to loosen the cake, then flip the cake onto a plate to remove it from the pan.
Make the frosting by combining heavy cream, powdered sugar, and vanilla extract in a bowl. Beat on medium-high speed until firm peaks form, about 3 minutes. The peaks should be stiff and hold their shape when the whisk is lifted. Refrigerate, if needed, until ready to assemble.
To assemble, place the first layer on a plate. Use an offset spatula to spread a generous layer of whipped cream on top, scatter sliced mangoes over the cream, then cover with another layer of whipped cream. Place the second layer on top and cover the cake with whipped cream. Refrigerate for a few hours, then decorate with more mangoes before serving.