Preheat your oven to 350°F (175°C).
Cream together the unsalted butter and superfine sugar until light and fluffy. Add custard powder (or corn starch with vanilla), vanilla extract, and flour, mixing until a soft dough forms.
On a lightly floured surface, roll out the dough to about 1/4 inch thickness. Cut out circles using a cookie cutter or glass. Place them on a baking sheet lined with parchment paper.
Bake for 12-15 minutes, until the edges are lightly golden. Allow to cool completely on a wire rack.
Make the custard filling by beating room temperature butter until creamy. Gradually add powdered sugar, mixing until smooth, then blend in custard powder (or corn starch with vanilla).
Spread filling on the flat side of one biscuit and press another biscuit on top to create a sandwich. Repeat until all biscuits are filled.
Enjoy your Custard Creams with a cup of tea or as a sweet treat!
