In a heavy sauce pan, mix sugar and cocoa together evenly, getting most of the lumps out of the cocoa. Add the butter and milk and cook over medium heat until boiling. Stir constantly. Let boil for 1 minute.
Leave the heat on and then add peanut butter and vanilla. Stir until peanut butter is melted completely. Add oatmeal and stir (over heat) for another minute.
Drop by teaspoon fulls onto waxed paper. The reason I left the heat on during the whole process was I wanted the oatmeal to cook more. I don't like the taste of raw oatmeal in the cookies. For some reason, the extra cooking time makes them not set up so fast, which is also a good thing. They turned out so moist and not crumbly and everyone said they were better this way.
Tip for measuring peanut butter: Get a 4 cup measuring cup. Fill it with 3 cups water and drop peanut butter into water until water line hits the 4 cup mark. This is for one cup. If you need 2 cups, just put in 2 cups water and add peanut butter till it reaches the 4 cup mark.... etc. Pour off water and peanut butter will practically fall out of cup. No scraping and leaving lots of it behind.