Start by preheating your oven to 350°F. While it's warming, line your baking sheets with parchment paper—this is non-negotiable for even baking and easy cleanup. I typically use two standard 18-by-13-inch sheets, which gives me plenty of room to space the cookies properly.

In a medium-sized mixing bowl, whisk together the flour, baking powder, and salt. I like to whisk this combination for about 30 seconds to break up any small clumps and distribute the baking powder evenly throughout the flour. This ensures every cookie rises uniformly. Set this bowl aside—you'll add it to your wet ingredients in just a moment.

This step is where the magic happens. In your large mixing bowl, combine the cool room-temperature butter and 1¼ cups sugar. Using an electric mixer fitted with a paddle attachment on medium-high speed, beat this mixture for 2 to 3 minutes. You're looking for a transformation—the mixture should go from grainy and dense to pale, light, and noticeably fluffy, almost like fluffy clouds. This is the creaming process, and it's what gives these cookies their signature tender texture. Stop the mixer halfway through to scrape down the sides and bottom of the bowl with a rubber spatula. This ensures all the sugar gets fully incorporated into the butter.

Once your butter-sugar mixture looks light and fluffy, add the whole egg and the single egg yolk. Beat on medium speed for about 30 seconds until the eggs are fully incorporated. Add the vanilla extract and beat for another 15-20 seconds. The mixture should be smooth and slightly pale. Again, scrape down the sides of the bowl to make sure everything is evenly combined. Here's a pro tip from my kitchen testing: if the mixture looks slightly separated or curdled at this point, don't panic. This sometimes happens, especially in cooler kitchens. It will come together beautifully once you add the flour.

Reduce your mixer speed to low or medium-low. Slowly pour in your flour mixture while the mixer is running. Beat just until combined—this should take about 30-45 seconds. You're looking for a dough that just comes together without any visible streaks of flour. Don't overmix at this point, as that can develop the gluten and make your cookies less tender. The dough should be soft but not sticky, and it should hold together when you squeeze a small piece in your hand.

Pour the remaining ¼ cup sugar into a shallow dish—a small bowl or plate works perfectly. Using a large spring-loaded cookie scoop (about 3 tablespoons each), divide your dough into balls. Working with one ball at a time, roll it in the sugar until it's evenly coated on all sides. This creates a beautiful crystallized exterior and adds pleasant texture contrast. Place each sugared ball on your prepared baking sheet, spacing them about 2 inches apart. They'll spread slightly as they bake, so don't crowd them. Using the bottom of a measuring cup, gently flatten each ball slightly—you want them about ½ inch thick before baking.

Bake your cookies for 10 to 12 minutes, until they're set and just beginning to develop light golden-brown color around the edges. The centers will still look slightly underbaked—this is exactly what you want. The cookies continue cooking on the hot baking sheet after you remove them from the oven. Let the cookies cool on the baking sheet for exactly 5 minutes. This resting time allows them to firm up enough to transfer without breaking but not so long that they harden completely. Then transfer them to a wire cooling rack and let them cool completely before storing.