Preheat the oven to 350°.
Using a paddle attachment, combine the dry ingredients in the bowl of an electric mixer. Add the egg and vanilla extract and mix until just combined. Add in the cubed butter—piece by piece—until the dough just comes together. Don’t overmix or the cookies will be too dense! Pat the dough into a rectangle, wrap in plastic or parchment paper and chill for at least 2 hours.
When ready to bake, cut the dough into 3 even strips and roll each strip into a log on a floured surface. Slice each log into 1-inch rounds, then roll the rounds into balls. If the dough is too soft, refrigerate again until well chilled. Roll each ball gently from the ball to the heel of your hand several times, until each ball forms a log and the ends taper slightly. Don’t press too hard. Bend the edges of each cookie in to create a crescent shape.
Once all the cookies are shaped and on a baking sheet lined with parchment paper or Silpat, refrigerate again until chilled, then bake for about 10 minutes until the edges are just lightly golden—rotating the sheet halfway through baking. Allow to cool for 10 minutes, then dust with confectioners’ sugar using a fine-mesh sieve and allow to cool completely.