Instructions

1. Preheat oven to 180 C (350 F) standard / 160 C (320 F) fan-forced. Line two baking trays with baking or parchment paper.
2. In a large mixing bowl, beat butter with an electric mixer on medium speed for 1 minute or until creamy. Add flour, salt, sugar and custard powder and beat until a soft cookie dough forms.
3. Roll roughly two teaspoons of cookie dough in your hands to form a ball and place on prepared tray. Repeat with remaining cookie dough. Press down on each cookie using a fork.
4. Bake cookies for approximately 12 minutes. Leave to cool slightly before transferring to a wire rack to cool completely.
5. To make the frosting, place butter in a large mixing bowl and beat with an electric mixer on medium speed until pale and creamy.
6. Add vanilla, half the sugar and one tablespoon of milk and beat until combined. Add the remaining sugar and another tablespoon of milk and beat until smooth.
7. If the frosting is too thick, add an extra tablespoon or two of milk. Add buttercream to a piping bag fitted with a large round tip. Pipe buttercream onto one cookie. Add another cookie on top. Repeat with remaining cookies.