Step 1: In a large mixing bowl, using an electric mixer, cream together the softened unsalted butter and granulated sugar on medium speed until light, fluffy, and pale yellow, about 3-5 minutes. Scrape down the sides of the bowl as needed.
Step 2: Beat in the large egg and pure vanilla extract until just combined. Do not overmix.
Step 3: In a separate medium bowl, whisk together the all-purpose flour, baking powder, and salt until well combined.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined and no streaks of flour remain. Avoid overmixing.
Step 5: Divide the dough in half. Flatten each half into a disc, wrap tightly in plastic wrap, and refrigerate for at least 1-2 hours, or preferably overnight. Chilling is essential for preventing spread.
Step 6: Preheat your oven to 375°F (190°C). Line baking sheets with parchment paper or silicone baking mats. On a lightly floured surface, roll out one disc of chilled dough to about ¼-inch thickness. Use your favorite cookie cutters to cut out shapes. Gather scraps, gently re-roll, and cut more cookies.
Step 7: Carefully transfer the cut-out cookies to the prepared baking sheets, leaving about 1 inch between each. For best results, chill the cut-out cookies on the baking sheets for another 10-15 minutes before baking.
Step 8: Bake for 8-10 minutes, or until the edges are very lightly golden and the centers still look soft. Baking time will vary based on oven and cookie thickness.
Step 9: Remove the baking sheets from the oven and let the cookies cool on the sheets for 5 minutes before transferring them to a wire rack to cool completely. Once completely cool, they are ready for decorating.