In the bowl of a stand mixer, beat together the butter and sugar, on medium speed, until creamy, about two minutes. Add in the egg and vanilla and continue beating, until the mixture is fluffy, about two more minutes.
Next, add the salt, matcha and baking powder. Blend until incorporated, about 30 seconds.
Lastly, add in the flour. Beat just until the majority of the flour is incorporated. Finish stirring by hand, so as not to overmix.
Gather the dough into a disk and wrap it tightly in plastic wrap. Refrigerate for at least an hour, or up to two days.
When you’re ready to make the cookies, allow the dough to sit out for about 10 minutes. Meanwhile, preheat the oven to 350F degrees. Line a baking sheet with a silpat mat and set aside.
Once the dough has softened slightly, roll it out, on a well-floured surface, to about a 1/4” thick. Cut out cookies using a shamrock cookie cutter. Place on the lined baking sheet, leaving about an inch between each cookie.
Bake for 8-10 minutes, or until the edges are just slightly browned.Transfer the cookies to a baking rack and allow to cool.
Once the cookies have cooled, melt the chocolate. Dip the cookies in, either completely or halfway, and then place them back on the baking rack to allow the chocolate to harden.
If desired, add on sprinkles, or, make green chocolate by adding a few drops of green food coloring to some of the melted white chocolate, and then drizzle that on to the cookies.