Preheat the oven to 215˚C. Dampen two baking trays with a bit chilly water. Line a 20cm sq. cake tin.
Roll out the tough puff pastry to 3mm thickness or use the prepared-rolled pastry sheets. Reduce into two 25cm squares. Tidy any tough edges.
Place the pastry on the ready baking trays and prick completely with a fork throughout. This can discourage the pastry from rising an excessive amount of because you need flat, flaky sheets. Chill on the trays for quarter-hour.
Bake for about 20 minutes till darkish golden brown. Fastidiously flip every bit of pastry over after quarter-hour to make sure it’s cooked proper by. Place on a wire rack to chill.
In a saucepan, combine the custard powder, icing sugar and ¼ cup milk to a easy paste.
Add the remaining milk, butter and egg and prepare dinner, stirring, till the combination may be very thick.
Cowl with a humid paper towel or plastic wrap pressed onto the custard floor to stop pores and skin from forming. Depart till cool however nonetheless pourable.
Trim the cooked pastry sheets to 20cm squares. Match one within the base of the tin, pour over the cooled custard and high with a second sq. of pastry.
Depart to set for 20 minutes after which ice with Icing or mud with icing sugar.
Icing:
Mix icing sugar and butter with a bit water, mixing till you may have a easy icing.
Unfold excessive pastry layer and refrigerate for an additional half-hour, till chilly and set.
Use a serrated knife to fastidiously lower into squares.
Take pleasure in!