Start by whisking egg whites with granulated sugar over a simmering water bath until frothy, about 4-5 minutes.

Transfer the mixture to a stand mixer and whip on high speed until stiff peaks form, about 6-8 minutes.

Gently fold in sifted almond flour and powdered sugar until the batter flows like lava.

Line a baking sheet with parchment paper and fit a piping bag with a round tip.

Pipe uniform circles onto the prepared sheet and let sit at room temperature for 20-40 minutes.

Preheat oven to 300°F (150°C) and bake the macarons for approximately 18 minutes.

In a saucepan, combine mangoes, sugar, and lemon juice; cook until soft, about 5-7 minutes.

Mix cornstarch with cold water, add to the mango mixture, and cook until thickened, about 2-3 minutes.

Beat unsalted butter until fluffy, then gradually add powdered sugar; fold in cooled mango jam.

Assemble the macarons by piping mango buttercream and mango jam between shells.