In a 2-quart (or larger) saucepan, add the butter, sugar, cocoa powder, and milk. Stir occasionally and bring the mixture to a full boil. Once it’s boiling, set a timer for 1 minute.
After 1 minute, turn off the heat and add in the peanut butter, vanilla, and salt. Stir until the peanut butter is completely melted and smooth.
Add the oats and mix until they’re fully coated in the peanut butter chocolate mixture. Let the mixture rest for about 5 minutes so the oats can absorb the ingredients. This will make the cookies easier to scoop.
Line two baking sheets with parchment paper. Drop about 2 tablespoons of the mixture per cookie onto the sheets. Leave as mounds or gently flatten into a level disc.
Chill the cookies in the fridge for 45-60 minutes, or let them set at room temperature for about 90 minutes. They’ll be soft, but not sticky, and you can pick them up easily without getting your fingers all dirty.
Store the cookies in an airtight container either at room temperature or in the fridge. If you live in a humid climate, I recommend keeping these chocolate no-bakes in the fridge.