Preheat the oven to 350 F. Line 2 baking sheets with parchment paper or silicone baking mats.
Microwave the butter in a large, microwave-safe bowl for about 40 seconds. Butter should mostly melted.
Whisk the butter until it is completely melted.
Add the sugars; mix until well-combined.
Stir in vanilla and egg until incorporated.
Add the flour, cocoa powder, baking soda, and salt. Please read the recipe note about properly measuring flour.
Mix dough until just combined. Dough should be soft and a little sticky but not overly sticky.
Stir in peanut butter chips and chopped peanuts.
Scoop out 1.5 tablespoons of dough (medium cookie scoop) and place 2 inches apart on baking sheet.
Bake for 7-10 minutes, or until cookies are set. They will be puffy and still look a little underbaked in the middle.
Butter: This recipe uses melted butter. I prefer to use salted butter, but you can use unsalted butter if you prefer.
Sugars: This recipe uses both brown sugar and granulated (white sugar). You can use either dark or light brown sugar. Dark brown sugar will give you a slightly richer flavor.
Measuring Flour: If you aren’t weighing your ingredients, I can’t recommend that enough. If you are using measuring cups, be sure to sift or stir the flour before measuring. Flour packs easily and using too much flour in cookies will give you dry, crumbly dough and cookies that don’t spread.
Salt: If you'd like to use kosher salt in place of the table salt, use 1/2 teaspoon.
Peanut Butter Chips: I use plain peanut butter chips. There are also mixes that contain both peanut butter and semisweet chocolate chips. You can use another whichever you prefer.
Peanuts: I use lightly salted peanuts to give the cookies more salty/sweet flavor. You can use regular salted or unsalted depending on how much salt you'd like in your cookies.
Baking: One of the keys to make soft cookies is slightly underbaking the cookies. This means that the edges should look set but the middles should still look puffy and soft.