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.
2 ½ cups (300g) all-purpose flour*, ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon 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.
¾ cup (170g) unsalted butter, 1 ¼ cups (250g) granulated sugar, 1 large egg, 1 egg yolk, 2 teaspoons vanilla extract
Add the dry ingredients to the wet and mix on low speed until combined. It will be a fairly firm dough.
Roll the dough into 1-inch balls. If desired, roll each ball in granulated sugar. Place on the parchment-lined baking sheet, about 3 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 overbake. (The cookies may still be slightly puffy when you take them out of the oven and will flatten more as they cool on the baking sheet.)
¼ cup (50g) granulated sugar