Preheat the oven to 400℉. Grease a baking sheet or line with parchment paper. Set aside.
Add butter and sugar to the bowl of a stand mixer (or use a large mixing bowl and electric hand mixer). Mix on high speed for about 2 minutes, until mixture is light and creamy.
Add egg, milk and vanilla extract and mix on medium speed to combine. If using, add food coloring and mix on medium speed to combine..
Add flour and baking powder and mix on low speed, until just combined. *Avoid over mixing, which can cause dry/crumbly cookies.
On a lightly floured work surface, roll the dough to ¼-inch thickness. I recommend this adjustable rolling pin for perfectly rolled cookies.
Use a shamrock-shaped cutter to cut out the cookies. Using a thin metal spatula, carefully transfer cookies to prepared baking sheet. If desired, sprinkle colored sugar or sprinkles on the top of cookies.
After placing the first batch in the oven, gather your scraps, form into a ball and roll/cut out more cookies. Repeat until all dough is used.
Bake in preheated oven for 5-8 minutes, until very lightly browned on edges. The tops may not brown much, and this is okay.Cookie Baking Tip: Add a piece of scrap dough to your baking sheet. You can lift this scrap piece to check if the bottom of your cookies is golden brown rather than damaging one of your perfect cut out cookies!
Remove from oven and let the cookies cool on pan for 3-4 minutes, until they’re firm, then transfer to a wire cooling rack to finish cooling.
Notes
To use baking soda as a substitute for baking powder, mix ¾ teaspoon cream of tartar and ½ teaspoon baking soda to substitute for 1 ½ teaspoons baking powder.Watch when baking! These go from perfectly golden brown to burnt quickly!Measure your ingredients correctly - It is super important to measure your ingredients correctly, specifically the flour! Check out this tutorial on how to measure flour correctly.Use flour when rolling out the dough. Make sure to flour your work surface and the top of the dough/rolling pin when rolling out the cookie dough. Otherwise the dough will stick/be difficult to transfer to the baking sheet.Storing/Freezing Baked CookiesStore baked shamrock cookies in an airtight container for up to 2 weeks. Placing a piece of bread in the container will help keep the cookies soft. Cookies may be frozen in an airtight container for up to 3 months. Place squares of parchment paper or wax paper between each cookie to prevent them from sticking together.