Preheat the Oven - Position the rack in the center of the oven. Preheat to 350°F (177ºC). Line two large sheet trays with parchment paper and set aside.
Make the Dough - Using the paddle attachment on a stand mixer, cream the butter and sugar on medium speed until light and fluffy, about 1 minute. Add salt, vanilla, and egg. Mix on medium speed until combined, about 1 minute. Scrape down the sides of the bowl as needed. Gradually add the flour to the bowl, mixing on low speed for about 1 minute.
Pipe the Cookies - Scrape the dough into a piping bag fitted with a 1⁄2" star tip or desired tip. Pipe 1 ½ to 2" pretzel or wreath shapes onto the parchment paper-lined sheet trays, at least 2" apart.If desired, sprinkle the tops of the cookies with granulated sugar or large coarse sparkling sugar.
Bake - Bake one tray at a time. Bake until cookies are lightly golden on the bottom, about 11 to 13 minutes.
Let Them Cool - Leave the cookies on the baking sheet for 3 minutes, then transfer them to a wire rack to cool completely.
Notes
Use Softened Butter: The butter should be cool and give some resistance when poked.
Flour Selection: Gold Medal all-purpose flour was used in this recipe.
Vanilla Bean Substitution: Use 1 ½ teaspoon vanilla extract or paste
Work Quickly: The longer you let the dough sit in the piping bag, the thicker it becomes. Try to pipe right after making the dough if possible.
If Too Thick to Pipe: Shortbread cookie dough tends to be thicker than other piping dough. If needed, add 1 to 3 teaspoons of milk, 1 teaspoon at a time, and combine until just mixed.
If too Soft to Pipe: If the dough is too soft and does not hold its shape, gradually add 1 tablespoon (9 g) of all-purpose flour at a time, adding more as needed up to 1/4 cup (36 g). The dough typically gets thicker as it sits as the proteins absorb the moisture, so try to wait a few minutes between adding additional flour.
Storing: Store in an airtight container for up to 5 days, or freeze for up to 3 months.