Place the butter, sugar, cocoa powder, and milk in a large saucepan over medium heat. Bring to a boil over medium heat. Let boil for one minute without stirring.
Remove the mixture from the heat, and stir in the oats, peanut butter, and vanilla extract. Drop spoonfuls of the cookie dough onto a large plate. Place mini cadbury eggs on each cookie. Let sit until the cookies are completely set.