To make the dough, in a standing electric mixer or using a large bowl with an electric hand mixer, beat the butter until pale and creamy, about 2–3 minutes. Add the flour, icing sugar, custard powder or cornflour and the passion fruit flesh with seeds. Beat for another 2–3 minutes until smooth.
Line two baking trays with baking paper. Roll
To make the filling, place the butter in the bowl of the electric mixer and beat for a minute or two until creamy. Add the sugar and beat until smooth, about 2 minutes. Add the passion fruit pulp and seeds and beat again until smooth.
Sandwich the biscuits together using the passion fruit filling. Store in a covered container until ready to serve. These will keep for up to a week.