In a medium saucepan, combine the butter, sugar, milk, and cocoa powder.
Cook over medium heat, stirring occasionally, until the mixture comes to a rolling boil.
Let it boil for 1 minute, stirring frequently to avoid scorching.
Remove the saucepan from heat and quickly stir in the peanut butter, vanilla extract, and a pinch of salt until smooth.
Add the oats and mix well until fully coated with the chocolate mixture.
Drop spoonfuls of the mixture onto wax or parchment paper, spacing them apart to avoid sticking.
Allow the cookies to cool and set at room temperature for about 30 minutes, or place them in the refrigerator for quicker setting.
Once firm, store the cookies in an airtight container at room temperature or in the fridge.