Biscuit sponge cake:

• Pre-heat oven to 350F (conventional) and line a 9x13" tray with parchment paper
• Into the egg yolks, add 1/2 cup sugar, salt, and vanilla, and whisk for 1-2 minutes until light and fluffy
• Whisk in the milk, and then sift in the flour, cornstarch and baking powder. Whisk to combine. Do not overmix
• Separately, to the egg whites, add the cream of tartar and start whisking (with a clean whisk) on medium speed. Once the egg whites look white and frothy, start adding the remaining 1/4 cup sugar a little at a time while continuing to whisk. Keep whisking for a few minutes until a shiny, stiff and glossy meringue is formed
• Add a third of the meringue into the egg yolk mixture and gently fold it in with a spatula. You have to be extra gentle and work slowly, as you don't want to knock out the air we have whipped into the meringue. Then add the remaining meringue and fold in gently
• Transfer the batter to the pan, and bake for about ~15 minutes or until done
• Let the cake cool down

Mango lassi:

• Blend all ingredients together until smooth, then strain through a fine sieve mesh. Taste and adjust if needed

Mango three milk mixture:

• Whisk all ingredients in a bowl until combined. Taste and adjust sweetness if needed. Make sure the mixture is quite liquidy. If it is thick, add a bit more milk to it

Soak the cake:

• Use a skewer to poke holes throughout the cake, keeping it in the baking pan (these holes should be larger than a toothpick). Pour over about a fourth of the three milk mixture and wait until it is absorbed. If it has not absorbed in 20 minutes, you need to dilute the mixture with a bit more milk. Then add the remaining liquid in 2-3 steps and wait until it absorbs before adding more. Place the cake in the refrigerator for a few hours until the milk mixture is fully absorbed by the cake
• If you see after the first addition that the milk mixture is taking too long to soak in (over an hour), it might be too thick. Add more milk to the remaining mixture

Mango lassi whipped cream:

• Using the balloon whisk attachment of your stand mixer, whip up the heavy cream until it is thick. Add the remaining mango lassi a little at a time while continuing to whisk, and taste as you go. Stop whisking once the cream reaches firm peaks

Assemble:

• Spread a thick layer of the mango lassi whipped cream on the cake evenly. Decorate with more whipped cream (optional) and freshly chopped mango (more the merrier!)
• Serve and enjoy cold!