In a medium saucepan over medium heat, combine the salted butter, granulated sugar, unsweetened cocoa powder, and milk. Stir continuously until the mixture is smooth and begins to boil.
Once it reaches a rolling boil, let it boil for 1 minute without stirring.
Remove the saucepan from heat and stir in the vanilla extract and creamy peanut butter. Mix well until fully incorporated.
Gradually add the quick oats to the peanut butter mixture. Stir until all oats are evenly coated.
Using a spoon or cookie scoop, drop the mixture onto a baking sheet lined with parchment paper.
Allow the cookies to cool at room temperature for about 30 minutes, or until firm. Refrigerate to speed up the process if necessary.
