Add the butter, sugars, cocoa powder, and milk to a medium sauce pan. Measure out all of the other ingredients and have them ready to go near the stove.

Cook the butter mixture over medium-high heat, stirring, until the butter melts and the mixture comes to a full rolling boil even in the center (not just around the edges). Once the mixture is at a rolling boil, stop stirring and cook for exactly 1 minute.

Remove from heat and working quickly, stir in the peanut butter, followed by the oats, vanilla, and salt, until completely mixed.

Let the mixture rest for 2-3 minutes for the oats to soak up a bit of moisture while you line a baking sheet with parchment paper. (Otherwise your cookies will be quite thin.)

Scoop 2-tablespoon-sized balls of the mixture onto the prepared baking sheet. I recommend a medium cookie scoop. If your cookie spreads too much, let the mixture cool for another minute. Working quickly, scoop all of the cookies onto the baking sheet with a cookie scoop or spoon, shaping them into mounds, if needed.

Before removing the cookies from the baking sheet, let them cool completely until firm to the touch, 1-2 hours at room temperature or 15-30 minutes in the fridge.

Store on the counter in an air-tight container for up to 3 days or in the fridge for a week. Enjoy straight from the fridge or at room temperature.