Preheat oven to 375 and line a baking sheet with parchment paper/spill mat or non-stick spray
In a medium sized bowl combine flour, cornstarch, baking powder, baking soda and salt.
In a stand mixer, or using electric beaters, combine the peanut butter and sugars.
Next add in the egg, yolk and vanilla. Mix until combined.
Add flour mixture to the peanut butter mixture and beat together until uniform.
Take ~2 tbsp of dough and form it into balls. Place ~2 inches apart on a cookie sheet.
Dip a fork into a small bowl of sugar and then press an "X" pattern on top.
Bake cookies for 9 minutes.
Allow cookies to cool fully and enjoy!