Prepare the baking surface: Line two baking sheets with parchment paper or wax paper.
Cook the chocolate mixture: In a medium saucepan, combine butter, sugar, milk, cocoa powder, and salt. Place over medium heat and stir until the butter is melted.
Bring to a boil: Once the mixture starts boiling, stop stirring and allow it to boil for 1 minute exactly.
Add peanut butter & vanilla: Remove from heat. Stir in peanut butter and vanilla until smooth and fully combined.
Mix in oats: Add oats and stir until well coated in the chocolate mixture.
Scoop cookies: Drop spoonfuls (about 1–2 tablespoons each) of the mixture onto the prepared baking sheets.
Cool & set: Allow cookies to cool at room temperature for 20–30 minutes until firm.
Enjoy: Once set, transfer to an airtight container or enjoy immediately.