Line a baking sheet with wax paper or parchment.
Bring the sugar, milk, butter and cocoa to a boil in a medium saucepan over medium heat, stirring occasionally, then let boil for 1 minute. Remove from the heat. Add the oats, peanut butter, vanilla and salt, and stir to combine.
Drop teaspoonfuls of the mixture onto the prepared baking sheet, and let sit at room temperature until cooled and hardened, about 30 minutes. Refrigerate in an airtight container for up to 3 days.