In a large bowl, cream the softened butter and sugar on medium speed until pale and fluffy, about 2 minutes.

Add the egg and vanilla, then beat on low just until smooth, about 30 seconds.

With the mixer on low, add the flour and salt, stopping when streaks of flour remain. Fold the rest by hand with a spatula.

Press the dough into two flat discs, wrap in plastic, and refrigerate for at least 1 hour.

Preheat oven to 350°F. Roll one disc ¼‑inch thick between parchment, cut shapes, and place on a parchment-lined sheet. Bake 8 to 10 minutes until edges are just set.

Cool on the sheet for 5 minutes, then transfer to a rack. Decorate cooled cookies with icing, glaze, or sprinkles.