1. Place oven racks in the upper and lower 1/3's of the oven. Pre-heat oven to 325º F. Cover cookie sheet with parchment paper.
2. Whisk flour, baking powder and salt in a medium bowl. Set aside.
3. Blend together butter and sugars until smooth.
4. Add egg, yolk and vanilla. Mix until incorporated.
5. Add dry ingredients and mix until just combined.
6. Stir in chips and optional nuts.
7. Form your balls whatever size you like, CI recommends 1/4 cup as these will give more structure to your cookie. I use a 1 1/4" cookie dough scoop. Evenly space on each cookie sheet, approximately 2" apart.
8. Bake for 12-15 minutes, rotating front to back and top to bottom after 6 minutes. Adjust according to how large your cookie balls are. Cool on sheets to maintain chewy texture.