Banana custard slice

1. Grease a 23cm square cake pan. Line with baking paper, extending 5cm above edges.

2. Process butter, sugar, flours, milkshake powder and water for about 2 minutes. Turn out onto a lightly floured surface. Shape into a square. Roll out between two sheets of baking paper until large enough to line base of pan.

3. Cook in a moderate oven (180°C) for 30 minutes. Cool.

4. To make custard, blend custard and milkshake powders with cup milk. Heat remaining milk in a saucepan until hot. Whisk in custard mixture over a low heat until boiling and thickened. Pour over pan. Smooth surface. Refrigerate, covered, for 2 hours.

5. Arrange bananas over custard. Dissolve jelly crystals in water in a heatproof jug. Pour over bananas. Refrigerate for 2 hours.

6. Cut into squares to serve.