Step 1

Bring 3½ cups of the milk to the boil in a saucepan.

Step 2

Mix custard powder, sugar and vanilla in a bowl with the remaining milk, then add the boiling milk while mixing continuously.

Step 3

If the custard doesn't thicken enough, return to the saucepan and bring to the boil, stirring, until thick.

Step 4

Layer biscuits in a 25 cm x 30 cm Swiss roll pan and pour over custard.

Step 5

Top the custard with another layer of Sao biscuits.

Step 6

Refrigerate and then ice with passionfruit icing.