Step 1

Grease a 3cm-deep, 20 x 30cm slice pan. Line the base and 2 long sides with baking paper, allowing the paper to overhang the sides.

Step 2

Place half the biscuits over the base of the prepared pan.

Step 3

Place the custard powder and 125ml (1/2 cup) milk in a saucepan. Whisk until smooth. Pour in the remaining 3 1/2 cups milk. Add the caster sugar then place the pan over medium heat. Cook, stirring constantly, for 5 minutes or until the custard comes to the boil. Cook, stirring, for 2 minutes or until thickened. Stir in the lemon rind then remove pan from heat. Cover the surface of the custard with plastic wrap. Set aside for 30 minutes to cool slightly.

Step 4

Pour the warm custard over the biscuits in the pan. Top with another layer of biscuits. Place in the fridge for 4 hours or until set.

Step 5

Dust the top of the slice with icing sugar. Use a sharp knife to cut the slice into even pieces, using the shape of the biscuits as a guide. Serve.