Separate the eggs. Keep the egg white bowl cool in the fridge.

In a clean bowl, bring together egg yolks and sugar, use a hand mixer to beat until light and fluffy and turns into pale yellow. Add in cake flour, mix well and set aside.

In a pot, bring together unsalted butter, salt and milk. Heat until boil. Pour the liquid into the batter while using a whisk or a hand mixer to mix them together. Pour all the batter back into the pot, keep mixing and stirring the batter over medium heat until lightly thickened. Sift once and set aside.

Preheat the oven to 320℉(160℃). Line the baking tray (28*28*2.6cm) with parchment paper or baking mat.

Take the egg white bowl out of the fridge. Add in lemon juice, sugar, and vanilla extract, and use a hand mixer to beat until it forms soft peaks. Take a scoop of whipped egg white and gently fold it into the batter until just combined. Pour all the batter into the whipped egg white and gently fold the egg white into the batter until just combined. Pour all the batter into the baking tray, smooth it out and send in to the oven to bake for 25 minutes. Set the oven to 356℉(180℃) and let bake for another 10 minutes. Take the cake out of the oven and let it cool on the cooling rack.

In a clean bowl, bring together heavy cream and sugar, and beat until stiff peaks form. Transfer the whipped cream into the piping bag. Wash, peel and chop the mango into cubes.

When the cake is cool to touch, release the sides of the cake with an icing spatula, turn the whole cake pan upside down on the parchment paper. Take off the pan, and peel off the baking mat.

Piping in the whipped cream and place the mango cubes in it and cover the mango with whipped cream, shape the cake into a cake roll. Wrap it up with parchment paper and let set in the fridge to cool for 30 minutes. Slice and serve.