Line a baking sheet with parchment paper or wax paper and set aside.
Pre-measure oats and peanut butter into separate bowls, set aside.
In a medium saucepan, combine the butter, sugar, milk, and cocoa powder. Heat over medium heat, stirring frequently, until the mixture comes to a rolling boil. Let it boil for EXACTLY 1 MINUTE while continuing to stir.
Remove the saucepan from the heat and immediately stir in the peanut butter, vanilla extract, and a pinch of salt (if using) until smooth.
Fold in the oats until they’re fully coated with the chocolate mixture.
Using a spoon or cookie scoop, drop dollops of the mixture onto the prepared baking sheet. Let the cookies cool and set for about 30 minutes at room temperature, or speed up the process by chilling them in the refrigerator.
Once set, your cookies are ready to enjoy! Store leftovers in an airtight container for up to a week.