Place 1½ cups of old fashioned oats in a food processor and pulse 6–8 times to break down the oats into a much finer texture. Transfer the processed oats as well as the remaining 2 cups of oats to a large bowl and set aside.

Add butter, sugar, milk, cocoa and salt to a medium-sized saucepan and place over medium heat. Stir constantly to mix ingredients and prevent scorching. Bring mixture to a boil and reduce heat to medium-low. Allow mixture to boil for 1 full minute then remove from heat.

Add vanilla and peanut butter to saucepan and stir until peanut butter is completely blended. Pour mixture into bowl containing oats and stir until oats are evenly coated.

Scoop by heaping tablespoons full onto a sheet of waxed paper and allow cookies to cool until firm.