Prepare the Pan: Line a baking sheet with parchment paper or a silicone mat. Set aside.
Combine Base Ingredients: In a medium saucepan, melt the butter over medium heat. Add the sugar, milk, and cocoa powder. Stir until well combined.
Boil the Mixture: Bring the mixture to a rolling boil and let it boil for exactly 1 minute, stirring constantly.
Add Remaining Ingredients: Remove the saucepan from heat. Stir in the peanut butter and vanilla extract until smooth. Then, fold in the oats until fully coated.
Scoop the Cookies: Drop spoonfuls of the mixture onto the prepared baking sheet, spacing them about 1-2 inches apart.
Set the Cookies: Let the cookies cool at room temperature for 30 minutes, or until firm. For faster setting, place them in the refrigerator.