1. Cream the butter and sugar together until light and fluffy. Scrape down the sides of the bowl.
2. In a separate bowl, whisk together the flour and baking powder. Set aside.
3. Add the egg to the butter and combine until smooth. Scrape down the bowl again, then add the vanilla and mix well.
4. With your mixer going on low, add the flour to the butter mixture in two additions until it's combined. The dough may appear a bit crumbly at first, but dump the mixture out on to the counter and bring it together with your hands, kneading once or twice. Pat the dough into two disks, wrap each with cling film, and chill for about an hour.
5. When you are ready to bake the cookies, take the dough out of the fridge and let it sit on the counter for about 15 minutes. Pre-heat the oven to 350 F.
6. Roll out your dough on a lightly floured counter about 1/4 inch thick and cut with a 3 inch cookie cutter. Set the cookies about 1 1/2 inches apart on a baking sheet and bake for about 10-12 minutes until the bottoms are lightly golden and the tops are set.
7. Remove cookies to a wire rack and let cool to room temperature before icing.

Icing the cookies

1. Mix the icing sugar with 2 tbsp whipping cream. It might clump a bit at first but keep stirring it vigorously. You want the glaze to be loose enough that it spreads easily, but not soupy or so thick that it falls in clumps off a spoon. If you can make it *just* run from your spoon to the bowl that's probably good.
2. Ice the cookies, top with sprinkles, and set on a rack to dry for about 2-3 hours before packaging them in an airtight container. They will keep for about 3-4 days in the container, or up to 3 weeks in the freezer.