1-First, preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. This step sets the stage for even baking and prevents sticking, making cleanup easy.

2-Next, in a medium bowl, whisk together the dry ingredients like the 2 cups all-purpose flour, 1 teaspoon baking powder, 1/2 teaspoon baking soda, and 3/4 teaspoon fine salt to ensure they mix evenly.

3-Then, in a large bowl, cream the 9 tablespoons unsalted butter at room temperature with the 3/4 cup granulated sugar and 3/4 cup dark brown sugar until light and fluffy. Add in the 1 large egg, 1 large egg yolk, and 1 tablespoon pure vanilla extract, beating well to combine. Gradually fold in the dry mixture until just blended, being careful not to overmix for that ideal chewy texture.

4-Scoop the dough onto the prepared baking sheet, spacing them about 2 inches apart. For an extra touch, sprinkle with optional flaky salt before baking. Pop them in the oven for 10-12 minutes until the edges are golden. Let them cool on the sheet for a few minutes before moving to a rack this helps maintain their chewiness. If you’re adapting for dietary needs, swap ingredients at the right steps, like using flaxseed for the egg in vegan versions.