Place the softened butter and sugar into a large bowl and whisk (I use a hand whisk) until well combined. Add the egg or flax egg and the vanilla and whisk again to combine. It may look lumpy, that is fine. (You can use a stand mixer if you prefer)

In another bowl, whisk together the flour, salt and matcha powder until well combined.

Add the dry ingredients to the wet ingredients and fold together until combined and you cannot see any flecks of flour. I like to use my hands to do this.

Divide the dough into 2 and place each between two sheets of baking parchment paper. Roll each dough out until it’s about 1/4-inch / 5-6mm thick and then place in the fridge to chill for at least 2 hours but preferably overnight (I usually just stack them and place them onto a baking sheet to keep them flat in the fridge).

Preheat oven to 180˚c / 350˚f.

Using a round or shaped cookie cutter that is about 5cm / 2-inch in size, cut out shapes. Re-roll the dough scraps and cut out more shapes until you have used up all the dough. Keep the dough chilled at all times - I keep the cut out shapes in the fridge until it is their turn to bake.

Arrange the cookie dough onto a parchment paper lined baking sheet, leaving 1-inch/2-3cm between each cookie (they don’t expand much). Working with one sheet at a time, place into the oven and bake until you just see the edges turn golden, 10-11 minutes. Remove from the oven and while still hot, sprinkle over the sparkling sugar (if you don’t sprinkle them on while still hot, they won’t stick; alternatively, you can sprinkle them on before you bake)

Continue baking the remaining cookies.