First, beat the softened butter with caster sugar until the mixture is light and fluffy — about 1 to 2 minutes. This step traps air and gives the cookies a more delicate crumb.
Sift the plain flour and cornflour together. Then add them gradually (in 3–4 portions) into the butter mixture, stirring gently until a soft dough forms. Don’t overwork it.
Wrap the dough in cling film and refrigerate for about 30 minutes. This firms it, makes it easier to roll, and helps the cookies hold shape while baking.
On a lightly floured surface, roll out the chilled dough to just under 6 mm (¼ inch) thickness. Use cookie cutters to stamp out your desired shapes and place them onto baking trays.
Preheat your oven to 150 °C (≈ 300 °F) or 130 °C in fan mode. Bake until the edges are just becoming pale golden — typically 15–20 minutes depending on size.
Let the cookies rest on the baking sheet for 10 minutes, then transfer to a wire rack to cool completely. Dust with icing sugar or add sprinkles (or optional icing) as your finishing touch.