Combine butter, sugar, milk and cocoa in a medium saucepan.
Cook over medium-high heat until it comes to a boil. Let the mixture boil for 1 minute while stirring the entire time.
Remove saucepan from the heat. Add peanut butter and vanilla, stir to combine.
When the mixture is smooth add the oatmeal and stir so that the oats are completely coated.
Scoop 1.5 tablespoons of mixture at a time onto a parchment lined cookie sheet.
Let your classic no bake cookies cool until set. Serve and enjoy. Store cookies in an airtight container at room temperature for up to 3 days.