Cut the unsalted butter into small cubes and let it sit at room temperature for about 15 minutes until it's slightly softened but still cool—this helps it incorporate air more effectively. Using an electric mixer on medium speed, beat the butter and packed brown sugar together for 3–4 minutes until the mixture is light, fluffy, and pale in color. This creaming process is crucial because it incorporates air into the dough, which creates the tender, melt-in-your-mouth texture these cookies are known for. I like to use Kerrygold butter because its higher fat content makes the shortbread extra rich and flavorful.

While the mixer is still running on medium speed, pour in the vanilla extract and beat for another 30 seconds until fully incorporated. In a separate small bowl, whisk together the flour and salt. This ensures the salt is evenly distributed throughout the dough, preventing any salty pockets in your finished cookies.

Reduce the mixer speed to low and gradually add the dry ingredient mixture from Step 2, mixing just until the dough comes together. Don't overmix—stop as soon as no flour streaks remain. Divide the dough in half, then roll each half into an 8-inch log about 1.5 inches in diameter using your hands or a flat work surface. The logs should be relatively uniform so they bake evenly.

Pour the coarse sugar onto a shallow plate or small baking sheet. Roll each dough log in the coarse sugar, pressing gently so it adheres to the outside of the dough. The sugar will give the cookies a beautiful sparkly texture and sweet crunch when you bite into them. Wrap each log tightly in plastic wrap and refrigerate for at least 4 hours, or up to 24 hours. This chilling time is essential—it prevents the dough from spreading too much during baking and helps develop the cookies' flavor.

Preheat your oven to 350°F and line two baking sheets with parchment paper. Remove the chilled dough logs from the refrigerator and, using a sharp knife, slice each log into 12 equal pieces (about 2/3 inch thick). Arrange the sliced cookies on the prepared baking sheets, leaving about 2 inches between each cookie to allow for slight spreading. I like to score my logs with small notches before chilling so I know exactly where to cut for uniform cookies. Bake for 14–16 minutes until the edges are lightly golden brown but the centers still look slightly underdone—they'll continue to cook slightly on the pan after removal.

Remove the baking sheets from the oven and let the cookies cool directly on the pan for 5 minutes—this allows them to set up just enough to be handled without breaking. Transfer the cookies to a cooling rack to cool completely. They'll firm up as they cool and develop their characteristic shortbread crispness.