Place sugar, butter, and milk in a medium saucepan. Stir over medium heat.
Bring to a rolling boil, stirring constantly, and boil for exactly one minute.
Remove from heat and mix in cocoa powder and vanilla until smooth.
Stir in quick oats until fully coated and mixture is thick.
Drop spoonfuls onto waxed paper or parchment.
Let cool until firm (about 20-30 minutes at room temp or 10 minutes in fridge).
