Line two baking sheets with parchment paper and set aside.
In a medium saucepan, combine sugar, butter, milk, and cocoa powder.
Bring to a rolling boil over medium heat and cook for 1 minute.
Remove from heat and stir in peanut butter and vanilla until smooth.
Mix in the oats until fully combined.
Drop spoonfuls of the mixture onto the prepared baking sheets.
Let cookies cool and set at room temperature for 30 minutes or until firm.