1. Whisk together the flour and baking powder in a bowl. Set aside.
2. In a large mixing bowl, cream the softened butter, vanilla extract, and sugar.
3. Add the eggs one at a time, mixing after each addition until combined.
4. Add the flour mixture and mix until combined.
5. Knead until the dough is firm and no longer sticky, adding more flour if necessary. Avoid adding too much flour, as the dough will firm up after chilling.
6. Wrap the dough in plastic wrap and chill in the refrigerator for 1 hour.
7. Preheat the oven to 375°F. Line baking sheets with parchment paper.
8. Shape the cookies into 1-inch balls, or make swirls. For swirls, take small pieces of dough and roll them on a floured surface into strips about 6 inches long and 1/3–1/2 inch thick. Pinch one end and twirl the remaining strip around it to form a circle, then tuck the end underneath.
9. Place the cookies on the prepared baking sheets, spacing them about 2 inches apart.
10. Bake at 375°F for 8–10 minutes. The bottoms should be lightly browned while the tops remain light.
11. Transfer the cookies to a wire rack and let them cool completely before glazing.

Glaze

1. Combine the vanilla extract, milk, and powdered sugar. Mix until smooth. The glaze should be thick but still runny. If it is too thick, add more milk; if it is too thin, add more powdered sugar.
2. Dip the tops of the cooled cookies into the glaze and let excess glaze drip back into the bowl. Place the cookies on a cooling rack and add nonpareil sprinkles while the glaze is still wet. Allow the glaze to dry completely, about 30–60 minutes.