In a bowl, combine softened butter, 1 tablespoon (15ml) egg, sugar, cake flour, all-purpose flour, dry milk powder, vanilla extract and baking powder. Mix until well combined.

Transfer the dough onto a large piece of plastic wrap and flatten into a disc.

Wrap well and place into the fridge to chill for 10-15 minutes.

Bring a small pot of water up to a boil.

Add in tapioca pearls, cover with a lid and remove pot from the heating element.

Let it sit for 7-8 minutes.

Remove lid, and drain the tapioca pearls into a sieve.

Give the tapioca pearls a rinse under cold water, drain well and transfer into a heat-proof mixing bowl.

Whisk egg, sugar, salt, cornstarch, and vanilla extract into a heat-proof mixing bowl. Set aside.

In a small pot, heat up whole milk and evaporated milk, until scalding (and not boiling).

Temper the egg mixture by pouring the warmed milk gradually into the egg mixture while whisking constantly.

Transfer the warmed mixture back into the saucepan and cook, whisking constantly over medium-low heat, until thickened.

Once thickened, transfer the warm custard into the bowl with the tapioca pearls.

Gently incorporate the tapioca pearls with the custard.

Divide the tapioca custard mixture into lightly greased ramekins.

Use a sharp knife to score the tops of the cookie crust.

Lightly brush the tops of the cookie crust with the remainder of the beaten egg.

Place the ramekins on a baking sheet lined with parchment or aluminum foil.

Remove from oven and let cool 10-15 minutes before serving.