Begin by preheating your oven to 350°F (175°C) and line your baking sheets with parchment paper. Ensure your butter is at cool room temperature, between 65-68°F, for optimal results.
In your mixer, beat the butter alone for 2-3 minutes. Add the granulated sugar gradually and continue beating for 5-7 minutes until the mixture becomes extremely light, pale, and fluffy. Remember to scrape down the bowl several times during this process.
Add the vanilla extract and eggs, one at a time, beating until well incorporated. Scrape the bowl again to ensure even mixing.
In a separate bowl, whisk together the flour, cornstarch, and salt. Gradually add this dry mixture to your butter mixture, mixing just until combined. Be careful not to overmix once the flour is added.
Fill a piping bag fitted with a star tip. Important: Secure your parchment paper to the baking sheet using a tiny bit of dough in each corner (or use a silpat) to prevent it from moving while piping.
Pipe rosettes or your preferred shape onto the prepared baking sheets. I find it easier to pipe if the bag is, at most, half full. If you make floral shapes, add half a maraschino cherry (dried off so they don't bleed) in the center of each one. You can also decorate with sprinkles or nonpareils.
Bake for 12-14 minutes, or until the cookies are just barely golden at the edges. Let them cool on the baking sheet for 5 minutes before transferring to a cooling rack.
Optional: Dip in melted chocolate as desired after cooling and sprinkle with nuts or sprinkles while the chocolate is still wet.