Preheat the oven to 350F then line a baking sheet with parchement paper and set aside.
Cream the butter, peanut butter, brown sugar, and granulated sugar together then add in the egg yolk and vanilla and mix to combine.
Fold in the flour, baking powder, baking soda, and salt.
Scoop the dough onto a baking sheet, flatten it to about 1 inch in thickness, and bake for about 13-14 minutes, you want the edges to be lightly golden and the center to still be a bit underbake (don't worry, it will continue baking as it cools down).
Let it cool down on the baking sheet for a few minutes before enjoying!
Notes
The nutritional value are for 1/4 of the cookie. If you have half the cookie take the nutritional value for one serving x2 and if you have the whole cookie just take the nutritional value for one serving x4.
How to store this giant peanut butter cookie?
If you have any cookies left then you can place them in an air-tight container and store them at room temperature for up to 4 days.I definitely doubt you'll have any left!