Preheat the oven to 375°F. Line a baking sheet with parchment paper.
In a clean bowl, sift flour, baking soda, baking powder, and salt. Set aside.
In another bowl, beat unsalted butter, peanut butter, and brown sugar by using an electric mixer. Beat on low for 5 minutes or until the butter is fluffy and pale in color.
Add egg and vanilla extract to the butter. Continue to mix for another 5 minutes or until the egg disappears into the butter.
Add the flour mixture to the butter and beat on low. You can use a spatula to mix the flour into butter if you find it easier for you. You should end up with a rather thick batter.
Using a tablespoon, take out balls of dough and place them on the lined baking sheet, about 2 inches apart from one another.
Press the fork tines twice on each dough ball to flatten the cookies while making a hashtag-like pattern. (this step is optional)
Place the tray in the freezer for at least 15 minutes to firm up (or 30 minutes in the fridge).
Preheat the oven at least 10 minutes before baking.
Put the cookie tray in the oven and bake for 10 minutes.
Once the time is up, remove from the oven and allow to cool completely on a wire rack before serving.