Add in the egg yolk, peanut butter, butter, , both sugars, and vanilla to a stand mixer bowl or a medium bowl. Beat everything together using a hand mixer or a stand mixer on medium-high speed until smooth and creamy. Make sure to stop and scrape the sides of the bowl as you go.
Add in the flour, baking soda, a pinch of salt, and the chopped peanuts to the wet mixture and beat again on low speed just until combined. Do not over mix!
Using a small cookie scoop, measure out 10 equally-sized cookie dough balls and place them on a parchment lined baking sheet. Flatten them slightly using your fingers and place then baking sheet in the freezer for a least an hour. DO NOT skip this step otherwise the cookies will spread too much and we do not want that.
After the cookies have been in the freezer for 55-60 minutes start preheating the oven to 350F. Line another baking sheet with parchment paper or silpat and set aside.
Coat the cookies in granulated sugar and place them on the new parchment lined baking sheet. Make sure to place the cookies at least 2 inches apart because they will spread quite a lot.
Bake for 12-15 minutes or until the edges are set and the tops look like they're just about to be set. You do not want to over bake the cookies because they will lose that perfectly soft attribute.
Let the cookies cool down for 15-20 minutes on the baking sheet before eating!