Line two baking sheets with parchment paper, wax paper, or foil.
Combine sugar, butter, milk, cocoa powder, and salt in a saucepan over medium-high heat. Bring to a boil, then let boil undisturbed for 1 full minute.
Remove from heat and stir in vanilla and peanut butter, then mix in oats. Use two spoons or a cookie scoop to portion onto lined cookie sheets. Let rest until set.
Notes
Make sure to use a saucepan that is large enough to fit all of the ingredients. You can also transfer the chocolate mixture into a mixing bowl to be able to add the oats.
If the cookie mixture seems too runny, you can add 1/4 to 1/2 cup of additional oats.
Nutrition information is an estimate based on online calculators and provided as a courtesy. Any nutritional information should be used as a general guideline only.