Preheat oven to 350 degrees. Grease or line baking sheets.
Whisk together flour, baking powder, baking soda and salt in a medium-sized bowl. Set aside.
Using a handheld mixer, beat butter, sugar and brown sugar just until smooth. (You may be tempted to use your stand mixer. Don''t. You''ll be less likely to overmix with the handheld mixer.) Add peanut butter and mix just until blended. Add egg and vanilla and mix just until blended.
Gradually add flour mixture, mixing (you guessed it) just until blended.
Using a cookie scoop or your hands, place tablespoon-sized balls of dough onto prepared pans. Using a fork, lightly make a crisscross pattern on the top of each cookie. Be careful not to over-flatten the cookies. Sprinkle each cookie lightly with sugar. (I like to use sanding sugar to give them a little extra sparkle.)
Bake cookies, one pan at a time, 14-16 minutes or until lightly browned. (Refrigerate the remainder of dough until ready to bake.) Cool on pan on wire rack for about 5 minutes. Then, transfer from pan to wire rack to cool completely.
