In a large bowl, beat the softened butter and granulated sugar together until light and fluffy, about 2-3 minutes. This creaming process incorporates air into the butter, which helps the cookies achieve their signature tender, crumbly texture. Add the finely grated key lime zest and beat for another 30 seconds to distribute the zest evenly throughout the butter mixture, ensuring the lime flavor is consistent in every cookie.

In a separate bowl, whisk together the all-purpose flour and salt. Add the dry ingredient mixture to the creamed butter mixture from Step 1 and stir until just combined—be careful not to overwork the dough, as this can develop gluten and make the cookies tough rather than tender and crumbly. The dough will come together quickly into a cohesive but slightly crumbly texture.

Turn the dough out onto a clean work surface and gently shape it into a log approximately 12 inches long and about 1.5 inches in diameter. Wrap the log in plastic wrap or parchment paper and freeze for at least 30 minutes—I find that freezing the dough makes it much easier to slice cleanly without the cookies falling apart or sticking to the knife.

While the dough freezes, preheat your oven to 375°F and line two sheet pans with parchment paper. This gives you time to prepare while the dough chills, keeping your workflow efficient and avoiding idle time.

Remove the frozen dough from the freezer and slice it into ¼-inch thick pieces using a sharp knife, wiping the blade clean between cuts to prevent sticking. Arrange the slices on the prepared sheet pans, spacing them about 1 inch apart, and bake for 12 minutes total, rotating the pans halfway through baking to ensure even browning. The cookies are done when the edges are golden brown but the centers remain pale—they'll continue to set as they cool.

Transfer the baked cookies to a wire rack to cool completely—this prevents condensation from making them soggy. While the cookies cool, whisk together the sifted powdered sugar and freshly squeezed key lime juice in a small bowl until smooth and spreadable. If the glaze is too thick, add lime juice a few drops at a time; if it's too thin, add more powdered sugar. The consistency should be like thick paint.

Once the cookies are completely cool, spread or drizzle the lime glaze evenly over each cookie using a small offset spatula or the back of a spoon. Let the glaze set for 15-20 minutes before serving—this final step adds brightness and a beautiful finish to the cookies.