Measure oats into a large bowl and set aside.
In a large skillet, combine butter, milk, sugar, peanut butter, and cocoa.
Stir together over medium heat (no higher) until fully combined. Don't quit stirring.
Once it is boiling while you stir (not just small bubbles around the edge, but a rolling boil) set the timer for 4 minutes.
Continue stirring constantly making sure to scrap the sides of the pan as needed.
When the timer goes off, turn off the heat and add vanilla. This will cause the mixture to bubble up. Stir to incorporate.
Add the oats and mix until completely covered. Try to work fast as the start to harden as they cool.
Scoop onto wax paper, using a greased cookie scoop if you have one.
Let fully cool, about 20 minutes.