Preheat the oven to 350F (180C). Line cookie sheets with parchment paper or silicone baking mats.
In a large bowl, beat together the butter, brown sugar and granulated sugar until creamy. You should no longer see lumps of butter.
Beat in the 2 eggs, additional egg yolk and vanilla extract.
Turn off the mixer. Add in the flour, and sprinkle in the baking powder, baking soda and salt. Mix together, starting with the electric mixer on a low speed and gradually increasing to medium speed until combined. The dough will be thick. When you squeeze it between your fingers, it shouldn't stay stuck to your fingers. If it does, beat in a little extra flour 1 tablespoon at a time.
Stir in the chocolate chips. I always stir in 2 cups and save the remaining ¼ cup for the tops of each cookie.
Form the dough into balls, with each dough ball using about 1½ - 2 tablespoons of dough each. I use a medium cookie scoop for this. Place about 2 inches (5 cm) apart on the lined cookie sheets.
Bake 1 cookie sheet at a time in the middle of the preheated oven. They will bake for about 11-13 minutes, or until the tops look just set.
Remove from the oven. Let the cookies cool on the cookie sheets. When the cookies are right from the oven, I like to place a few extra chocolate chips on the top of each cookie.