Mix the flour, corn starch, pinch of salt, baking powder, sugar, egg and cold butter (in small cubes).
Add some milk once you notice that the dough is a bit too dry. This does depend as well on the size of the egg. So if the dough is too wet, you can add some extra flour.
When the dough is mixed evenly; let it rest in the refrigerator for at least 30 minutes.
Cutting the Cookies.
Preheat the oven on 180 degrees Celsius or 356 degrees Fahrenheit.
Place some flour on the kitchen counter. Then use a rolling pin to roll out the dough to a 5mm or 0.2 inches thickness.
Use a scone or cookie cutter to make the cookies.
Bake these beauties on baking paper on the oven tray for about 10 minutes.
Glazing
Let the cookies cool before starting this step. When the cookies are warm, the glaze will slide off.
Whisk the egg white until a bit more foamy (however not until meringue stage). Then add the powdered sugar. Whisk until you have a firm white glaze.
Add any colorings if you like, and swirl them through the glaze by using a fork or wooden skewer.
Then dip the cookies topside down in the glaze. Use a fork to lift the cookies out of the glaze.
Try to let the glaze harden before consuming. However, I do understand that may be difficult ;)