Cover your counter or a baking sheet with wax paper to serve as the cooling surface for the cookies. Ensure the area is large enough to accommodate all the cookies.

In a 4-quart saucepan, combine butter, sugar, milk, and cocoa powder. Stir these ingredients together to create the chocolate base.

Place the saucepan over medium heat and stir continuously. Bring the mixture to a rolling boil and boil for 30-40 seconds. Overcooking may lead to dry, crumbly cookies, so time this step carefully.

Remove the saucepan from the heat. Stir in peanut butter until fully melted and smooth, then add vanilla extract and mix well.

Gradually add quick-cooking oats to the mixture, stirring to combine. Adjust the amount of oats to achieve your desired cookie consistency.

Using a tablespoon or cookie scoop, drop spoonfuls of the mixture onto the wax paper. Work quickly, as the mixture will begin to set as it cools.

Allow the cookies to cool and harden at room temperature for 20-30 minutes. Once set, they should easily peel off the wax paper. Store in an airtight container for up to a week.