Preheat the oven to 375°F (190°C) and adjust your oven rack to the middle position. Crucially, prepare baking sheets by leaving them plain and ungreased. Do not use parchment paper or silicone mats, as the dough must stick to the metal.

In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter and granulated sugar together on medium speed for 2 to 3 minutes, until the mixture is light and fluffy. Scrape down the sides of the bowl. Add the room temperature egg and the vanilla extract. Mix again until the egg is fully incorporated and the mixture is smooth.

In a separate bowl, whisk together the measured all-purpose flour and the salt. Reduce the mixer speed to low. Gradually add the flour mixture (about one third at a time) to the wet ingredients. Mix only until the flour is just combined and no streaks of dry flour remain. The dough should be soft, pliable, and hold its shape. Do not overmix.

If the dough is too warm, chill it for 10-15 minutes. Select your desired cookie disc shape and lock it into the cookie press barrel. Carefully fill the barrel with dough, packing it tightly to remove air pockets.

Place the base of the cookie press firmly against the ungreased baking sheet. Press the lever or turn the crank once to release the cookie. Lift the press straight up. If the cookie does not stick to the sheet, clean the sheet and ensure your dough is cool enough. Space cookies 1 to 2 inches apart. Immediately decorate with sprinkles or colored sugar, if desired.

Bake the cookies in the preheated 375°F (190°C) oven for 8 to 12 minutes. The cookies are finished when the edges are lightly set and the bottom rim just begins to turn a faint golden brown color, while the centers remain pale.

Remove the baking sheets from the oven and allow the cookies to cool on the sheets for 2 to 3 minutes before carefully transferring them to a wire cooling rack using a thin spatula. Allow the cookies to cool completely before serving or storing.