reheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a small bowl, whisk together the flour, cocoa powder, baking powder, and salt until well combined.
2 & ½ tablespoons all-purpose flour, 1 tablespoon unsweetened cocoa powder, ⅛ teaspoon baking soda, Pinch of salt
In a separate bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy. You can use a spoon or a small whisk for this.
1 tablespoon unsalted butter, 1 ½ tablespoons granulated sugar, ½ tablespoon brown sugar
Stir in the vanilla extract and egg yolk until fully incorporated.
¼ teaspoon vanilla extract, 1 egg yolk
Add the dry ingredient mixture into the butter mixture, stirring until just combined. Do not overmix. Fold in the chocolate chips, ensuring they are evenly distributed throughout the dough.
2 tablespoons semi-sweet chocolate chips
Form the dough into a cookie shape and place it onto the prepared baking sheet. Bake for 10-12 minutes, or until the edges are set and the center is slightly soft. Be careful not to overbake, as the cookie will continue to cook a bit after it's removed from the oven.
Allow the cookie to cool on the baking sheet for a few minutes, then transfer it to a wire rack to cool completely.