Combine the butter and sugar in the bowl of a stand mixer fitted with the paddle attachment and cream on high until homogenous (~3 minutes). Add the flour and salt, mixing until just combined (~30 seconds).
Remove the dough from the bowl and for it into a half-inch thick rectangle. Wrap in plastic and refrigerate until cold (~30 minutes).
Heat the oven to 350 degrees F.
Remove the dough from the refrigerator, unwrap it, and dust with a sprinkling of flour. On a floured surface, roll it out to a quarter-inch thickness with a rolling pin. Using cookie cutters, cut out shapes and carefully transfer to a baking sheet lined with parchment paper. Work quickly – the colder the dough, the easier it is to cut, transfer, and bake.
Bake the cookies for 8 to 10 minutes, until slightly golden around the edges. Cool completely on the baking sheet before glazing and decorating.
Frost the top surface of each cookie, then decorate with sprinkles (before the glaze hardens).
Cookie Glaze
2 cups confectioners’ sugar
1/4 cup milk
food coloring (optional)
Put confectioners’ sugar in a medium bowl. Whisking constantly, slowly stream in the milk until smooth.