Line a large baking sheet with foil, dull side up (this will provide the proper baking surface for the cookies to spread upon banging the pan).
In a small bowl, whisk together the flour, baking soda, baking powder, and salt.
1 ½ Cups Flour, 1/2 teaspoon Baking Soda, 1/2 teaspoon Baking Powder, 1/2 teaspoon Salt
Using a hand or stand mixer with the paddle attachment, cream the butter and then add peanut butter and cream until smooth (about 1-2 minutes on medium speed).
1/2 Cup Unsalted Butter, 1/2 Cup Creamy Peanut Butter
Then mix in the sugars until combined, about 1 minute. Scrape down the sides and bottom of the bowl and mix another minute.
1 ¼ Cup Sugar, 1/4 Cup Brown Sugar
With the mixer running, pour in the egg, vanilla and milk and mix until combined. Dump in the dry ingredients, scraping the edges as needed and mix on medium-low speed.
Allow the dough to rest at room temperature for 15-20 minutes. Preheat the oven to 350 degrees F.
Scoop the dough into a 1/4 cup or equivalent cookie scoop and roll in your hands.
Place 3-4 cookies on the baking sheet well spaced apart as they will spread quite a bit. Bake for 10 minutes, then remove the pan and slam it against the counter or stove top about 5 times until the edge deflate.
Place the pan back into the oven and bake for 2 minutes. Repeat the process. Continue baking in 2 minute intervals, banging between each, for a total bake time of about 16-18 minutes.
Stop once the cookies have completely spread and the edges turn a very light golden brown. Transfer to a cooling rack and repeat the process with the rest of the cookies.