01 - Whisk together flour, baking powder, and salt in a medium bowl until evenly combined.
02 - Beat butter and sugar in a large bowl on medium-high speed until light and fluffy, approximately 2–3 minutes.
03 - Add egg, vanilla extract, and almond extract if using. Mix until fully incorporated.
04 - Gradually add dry ingredients to wet mixture on low speed, mixing until just combined. Avoid overmixing.
05 - Divide dough in half and shape into flat disks. Wrap each disk tightly in plastic wrap and refrigerate for at least 1 hour.
06 - Preheat oven to 350°F. Line baking sheets with parchment paper.
07 - On a lightly floured surface, roll dough to ¼-inch thickness. Cut shapes using shamrock or round cookie cutters.
08 - Place cut cookies on prepared baking sheets, leaving 1 inch of space between each cookie.
09 - Bake for 8–10 minutes, until edges are just beginning to turn golden. Allow cookies to cool on baking sheet for 2 minutes before transferring to wire rack.
10 - Whisk powdered sugar, milk, and vanilla extract until smooth. Add green food coloring gradually until desired shade is achieved.
11 - Spread or pipe green icing onto completely cooled cookies. Top with sprinkles while icing is still wet. Allow icing to set completely before serving or storing.