Line two baking trays with paper and preheat your oven to 180 degrees.
Place 250g of the butter and a ⅓ cup of icing sugar into the bowl of an electric mixer and beat until it’s light and fluffy. With the mixer on a low speed, add the the vanilla essence and continue to mix until combined.
Remove the bowl from the mixer stand and sift in the self raising flour and custard powered and mix with a knife to form a dough.
Use a tablespoon to scoop up the mixture and shape into balls - you should have around 28.
Place the balls onto your baking trays and flatten slightly with a fork before placing the trays into the oven to bake for 20 minutes or until the cookies are slightly golden.
Allow the melting moments to cool slightly on the baking trays before carefully transferring to a wire rack to cool completely.
Once they have cooled, it’s time to make the filling. Add 60g of softened butter, ½ cup of icing sugar and 1 ½ tablespoons of lemon juice to the bowl of an electric mixer and beat until the mixture combines and is light and creamy.
Smear a little of the filling on the bottom of one biscuit before sandwiching it together with another.