Preheat the oven to 180°C conventional bake. Line 2 baking trays with non-stick baking paper.
Beat butter and Chelsea Vanilla Flavoured Icing Sugar with an electric mixer until creamy. Sift the flour and cornflour into the creamed mixture and mix well. The mixture will resemble breadcrumbs.
Roll heaped teaspoonfuls of mixture into balls and place on a baking tray. Press down lightly with a fork. Note: the biscuits won't spread very much.
Bake for 12-15 minutes until the biscuits are firm and lightly golden, but not brown. When biscuits have cooled, join in pairs with a generous spread or piping of the filling. Store in an airtight container.
Beat together butter, Chelsea Vanilla Flavoured Icing Sugar and hot water to form a smooth, spreadable consistency.