Preheat oven to 350 degrees F. Line two baking sheeting with parchment paper or silicone baking mats.
Beat the butter and sugar on medium speed until combined and fluffy, 1 to 2 minutes. Add the salt, vanilla and egg, and beat until combined, about 1 minutes. Reduce the speed to low and gradually add the flour until mostly combined. Give a final few stirs with a rubber spatula to ensure the flour is totally incorporated (the dough will be thick).
Transfer the dough to a decorating bag fitted with a large open star tip. Pipe the dough into 2-inch circles on the parchment paper or silicone baking mats. Sprinkle with sugar.
Bake, one pan at a time, until light golden brown, 15 to 17 minutes. Allow to cool completely before storing or serving.
Notes
Use good-quality butter (my favorite is Kerrygold).
You can substitute an equal amount of vanilla bean paste for the vanilla extract to give the cookies little flecks of vanilla.
My preferred piping tip for these cookies is the Ateco #827, but you can also use the Wilton 1M.
You can also use a cookie press to portion out the dough.
Allow the cookies to cool completely before eating or storing them.
The cookies can be stored in an airtight container at room temperature for up to 1 week, or frozen for up to 3 months.