Choc & passionfruit walnut bars

Grease a 19cm x 30cm lamington pan. Line base and sides with baking paper, extending the paper 3cm above the pan edges.

Melt butter in a saucepan, then remove from heat. Whisk in sugar and cocoa powder. Whisk in egg. 

Finely crush biscuits in a food processor, then place in a large bowl. Stir in coconut, walnuts and butter mixture. Press evenly onto base of prepared pan and refrigerate for 30 minutes.

To make filling, beat butter, custard powder and passionfruit pulp with an electric mixer until pale. Gradually beat in icing sugar and spread mixture evenly over base. Refrigerate until firm.

To make topping, place butter and chocolate in a heatproof bowl sitting over a saucepan of simmering water. Stir until smooth. Cool. Spread over filling. Refrigerate overnight, or until set.

Lift out of pan, then cut into bars to serve.