How to Make It
Heat oven to 375° F.
In a medium bowl, whisk together the butter, granulated sugar, vanilla, and eggs until blended. Add the flour, baking powder, and salt and mix until just combined (do not overmix).
With floured hands, roll level tablespoonfuls of the dough into balls and place on parchment-lined baking sheets, spacing them 2 inches apart. Bake until puffed and the bottoms are pale golden, 7 to 8 minutes. Transfer to a rack to cool completely.
Make the glaze: In a small bowl, whisk together the confectioners’ sugar, 2 tablespoons water, and the vanilla until the mixture forms a thick but pourable glaze (add more water if necessary).
Dip the top of each cookie into the glaze and let set, rounded side up, on a rack set over a piece of parchment paper. Sprinkle with non-pareils, if using. Allow the glaze to set, about 20 minutes. Store the cookies in an airtight container at room temperature for up to 5 days.