Preheat your oven to 350°F (175°C) to ensure even baking.
In a mixing bowl, whisk together the flour, baking powder, and salt until well combined.
In another bowl, beat the softened butter and granulated sugar together until light and fluffy, about 2-3 minutes.
Add the egg white and vanilla extract to the butter mixture, and beat until well combined.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
If desired, roll the dough into balls and roll them in powdered sugar before placing them on a baking sheet lined with parchment paper.
Bake the cookies for 8-10 minutes, or until the edges are just set and the tops look slightly cracked.
Let the cookies cool on the baking sheet for about 5 minutes before transferring them to a cooling rack.
In a mixing bowl, beat together the softened butter and sifted powdered sugar until smooth. Add milk or cream as needed for desired consistency.
Once the cookies are completely cooled, frost them and add sprinkles if desired.