**Prepare the Baking Sheet:** Line a baking sheet with parchment paper or a silicone baking mat. Set aside.
**Melt the Ingredients:** In a medium saucepan, melt the butter and peanut butter over medium heat. Stir until smooth and combined.
**Add the Wet Ingredients:** Stir in the milk, sugar, and cocoa powder (if using). Bring the mixture to a boil, stirring constantly. Once it reaches a boil, let it cook for 1-2 minutes while stirring.
**Add Vanilla and Oats:** Remove the saucepan from heat and stir in the vanilla extract and oats until the mixture is well combined.
**Form the Cookies:** Drop spoonfuls of the cookie mixture onto the prepared baking sheet. Use the back of the spoon to flatten them slightly, if desired.
**Let Them Set:** Allow the cookies to cool and set at room temperature for at least 30 minutes to an hour.
**Serve:** Enjoy immediately or store for later!
