1. Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. In a mixing bowl, whisk together flour and baking powder, then set aside.
3. In another bowl, cream together butter and sugar until light and fluffy.
4. Add eggs one at a time, mixing well after each addition.
5. Stir in anise extract and milk until combined.
6. Gradually add the dry ingredients to the wet mixture, stirring until a soft dough forms.
7. Cover the dough and chill it in the refrigerator for at least 30 minutes.
8. Roll the dough into small balls, about 1 inch in diameter, and place them on the baking sheet.
9. Bake for 8-12 minutes or until the cookies are set but still pale in color.
10. Let the cookies cool on the baking sheet for a few minutes before transferring to a wire rack.
11. In a small bowl, whisk together powdered sugar, milk, and anise extract to make the glaze.
12. Dip the top of each cooled cookie into the glaze, letting any excess drip off.
13. Place the glazed cookies on a wire rack and immediately sprinkle with rainbow nonpareils.
14. Allow the glaze to set completely before storing the cookies.
15. Store the cookies in an airtight container at room temperature or freeze for longer storage.