Place butter in the bowl of a stand mixer fitted with the paddle attachment. Add granulated sugar and powdered sugar. Beat on medium-high speed until pale and silky, about 3 minutes.

Reduce mixer speed to low. Add flour, cornstarch, and salt. Beat until just combined and the dough starts to come together, about 30 seconds.

Turn the dough onto a piece of parchment paper. Press into a disk about 1/2-inch thick, then roll out to 1/4-inch thickness. Transfer to a parchment-lined baking sheet and cut into your desired shapes, spacing cookies 1 inch apart. Prick each cookie with a fork.

Bake at 325°F (163°C) for 18 to 22 minutes, until edges are lightly golden. Let cookies cool on the pan for 5 minutes, then transfer to a wire rack to cool completely.