Step 1

Cream butter and icing sugar until pale and fluffy.

Step 2

In a separate bowl, sift custard powder and flour together.

Step 3

Continue beating butter mixture whilst adding the flour mixture, a couple of tablespoons at a time, until all combined.

Step 4

Roll into 24 balls, working quickly so the mixture remains cool.

Step 5

Refrigerate the uncooked biscuits for 3-5 minutes, so they hold their shape when cooked.

Step 6

With a fork, press down to flatten tops of the biscuits slightly and bake at 150C for 15-20 minutes.

Step 7

To make filling: Beat icing sugar, butter and vanilla together until light and fluffy.

Step 8

Divide the mixture across 12 of the biscuits and then join together with the remaining 12.