01 - Whisk together flour, baking powder, and salt in a medium bowl until evenly combined.
02 - Beat butter and sugar in a large bowl 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, mixing on low speed until just combined. Do not overmix.
05 - Divide dough in half, shape into disks, and wrap each portion in plastic wrap. 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 using shamrock or round cookie cutters.
08 - Place cookies on prepared sheets, spacing 1 inch apart to allow for slight spreading.
09 - Bake for 8–10 minutes until edges are just turning golden. Cool on baking sheet for 2 minutes, then transfer to wire rack to cool completely.
10 - Mix powdered sugar, milk, and vanilla extract until smooth. Add green food coloring to achieve desired shade.
11 - Decorate cooled cookies with green icing and sprinkles. Allow icing to set completely before serving.