Step 1

Preheat the oven to 180C/350F/Gas 4, and line a baking tray with parchment paper, or a silicone mat. Set aside.

Step 2

Whisk together the flour, baking powder, cornflour, baking soda, and salt. Set aside.

Step 3

Microwave the butter for 40 seconds, to just barely melt it. Whisk in the sugars until combined. Add the egg, and vanilla, and mix until combined. Add the dry ingredients, and mix until just combined. Fold in the sprinkles.

Step 4

Using a medium cookie scoop, scoop out 11 - 12 dough balls, then place on the prepared baking tray. Bake for 8 - 10 minutes. Allow to cool on the baking tray for 5 minutes before transferring to a wire rack to cool completely.

Step 5

Using a handheld or stand mixer fitted with the paddle attachment, beat the butter on medium speed until smooth and creamy.

Step 6

Add the icing sugar, heavy cream, vanilla extract, and salt. Beat on high speed for 3 minutes. Add more cream for a thinner frosting, or more icing sugar for a thicker frosting.

Step 7

Frost the tops of each cooled cookie, and decorate with sprinkles.