Preheat oven to 350° F. Line baking sheets with parchment paper.
In a medium mixing bowl, whisk together the flour, baking powder, baking soda and salt.
Use a stand mixer or hand mixer to beat together the butter and sugar until creamy, starting on low speed and then increasing the speed to medium-high. Add the egg, egg yolk and vanilla and mix in on medium speed until incorporated, scraping down the sides of the bowl as needed.
Add the dry ingredients to the wet and mix on low speed until combined.
Roll the dough into 1-inch balls or use cookie scoop for more uniformed cookies. Place on the parchment-lined baking sheet, about 2 inches apart. Bake one pan of cookies at a time, for 8-10 minutes, until tops are almost set and bottoms are light golden brown. For soft and chewy cookies, be careful not to over bake. (The cookies will be a little puffy when you take them out of the oven and will flatten more as they cool.)