Preheat the oven to 350°F (175°C) and line the 9x13-inch baking pan with parchment paper. In a large mixing bowl, combine the softened butter and granulated sugar using a silicone spatula until the mixture is light and fluffy, about 2-3 minutes, with a pale color and airy texture.
1 cup unsalted butter, 1 cup granulated sugar
Add the vanilla extract to the butter-sugar mixture and stir until evenly incorporated. In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, stirring with a spoon until just combined and a cohesive dough forms.
2 teaspoons vanilla extract, 2 cups all-purpose flour, ½ teaspoon baking powder, ¼ teaspoon salt
Spread the dough evenly into the prepared baking pan, smoothing the top with a spatula or the back of a spoon so that it is level and reaches the edges of the pan. Place the pan in the oven and bake for 20 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out clean. The surface should be firm and slightly cracked when done.
Remove the pan from the oven and allow the cookie bars to cool in the pan for about 10 minutes. Then, transfer them to a wire rack or cut directly in the pan into uniform squares or rectangles while still warm. The bars should have a lightly crisp edge with a tender, chewy interior.
Once cooled, serve the cookie bars as is, or optionally decorate with icing, sprinkles, or a dusting of powdered sugar for added flavor and visual appeal. Store leftovers in an airtight container at room temperature for up to 3 days.
