Cream the Butter and Sugar: In a large bowl using a stand mixer or an electric hand mixer, beat the 250g of softened butter and 140g of caster sugar together on medium speed for about 3-4 minutes. The mixture should become pale, light, and fluffy. Scrape down the sides of the bowl halfway through.

Add Wet Ingredients: Add the egg yolk, 1 tsp vanilla extract, and 1/4 tsp peppermint extract. Beat again for another minute until everything is well combined.

Combine Dry Ingredients: In a separate bowl, whisk together the 300g plain flour, 50g cornflour, and a pinch of salt. This helps distribute everything evenly.

Form the Dough: Gradually add the dry ingredients to the wet mixture in three additions, mixing on a low speed until just combined. Be careful not to overmix. The dough will look a bit crumbly at first. Use your hands to bring it together into a smooth ball.

Chill the Dough: Flatten the dough into a disc, wrap it tightly in cling film, and place it in the refrigerator to chill for at least 30 minutes. This step is essential to prevent the cookies from spreading while baking.

Roll and Cut: Preheat your oven to 180°C (160°C fan) and line two large baking trays with parchment paper. Lightly flour your work surface and rolling pin. Roll the chilled dough out to a thickness of about 5mm (the thickness of a £1 coin). Use a shamrock or round cookie cutter to cut out your shapes, placing them on the prepared trays with a little space between each one.

Bake the Cookies: Bake for 12-15 minutes, or until the edges are just beginning to turn a very pale golden colour. I find that they are ready when the surface looks matte and dry. They will still be soft when you take them out but will firm up as they cool.

Cool Completely: Let the cookies cool on the baking trays for 5 minutes before carefully transferring them to a wire rack to cool completely. They must be totally cool before you attempt to ice them.

Prepare the Icing: Sift the 200g of icing sugar into a bowl. Add 3 tablespoons of milk and mix until smooth. If it's too thick, add a little more milk, one teaspoon at a time, until you have a smooth, spreadable consistency. If you're using it, stir in a few drops of green food colouring.

Decorate: Once the cookies are cool, you can either dip the tops into the icing or use a small spoon to spread it over them. Immediately add your sprinkles before the icing sets. Let them sit at room temperature for about an hour for the icing to harden completely.