Instructions

1. Place 1 stick unsalted butter in the bowl of a stand mixer (or large bowl if using an electric hand mixer). Place 1 large egg on the counter. Let both sit at room temperature until the butter is softened. Meanwhile, place 1 1/2 cups all-purpose flour and 3/4 teaspoon baking powder in a medium bowl and whisk to combine.
2. Add 1/2 cup powdered sugar, 1/4 cup granulated sugar, and 3/4 teaspoon kosher salt to the bowl of butter. Beat with the paddle attachment on medium speed until lightened in color and fluffy, about 4 minutes. Scrape down the sides of the bowl and the paddle.
3. Add the egg, 1 tablespoon vanilla bean paste or vanilla extract, and 1 tablespoon milk or cream and beat on medium speed until combined, 30 seconds to 1 minute.
4. With the mixer on the lowest speed, gradually add the flour mixture and beat just until combined with no streaks of flour remaining, about 1 minute total.
5. Refrigerate the dough for 15 minutes. Meanwhile, arrange 2 racks to divide the oven into thirds and heat the oven to 350°F. Line 2 rimmed baking sheets with silicone baking mats or parchment paper.
6. Scoop out the dough with a 1/4-ounce scoop into about 40 portions (about 1 teaspoon each). Place on the baking sheets, spacing them evenly apart, about 20 per baking sheet. Wet your fingers and gently flatten each cookie dough ball until 1-inch wide and 1/4-inch thick.
7. Bake for 6 minutes. Rotate the baking sheets between racks and from front to back. Bake until the cookies are light golden brown around the edges, 4 to 6 minutes more. Refrigerate the remaining dough while the cookies bake.
8. Let the cookies cool on the baking sheets for 5 minutes. Transfer to a wire rack and let cool completely. Repeat baking the remaining dough on cooled baking sheets (you can reuse the parchment).