Melt the butter over medium heat and stir in the crushed gingernut biscuits. Press into the base and sides of a 20cm loose-base flan tin. Refrigerate until firm, approximately 30–40 minutes.
Combine the butter, sweetened condensed milk, and golden syrup in a saucepan, stirring over medium heat until boiling. Reduce the heat and stir constantly for 5 minutes.
(Further instructions like assembling and adding bananas, cream, and chocolate can be added if you want to provide them.)