PREP: Assemble all the ingredients, this recipe moves quickly! Line one extra-large (15x21-inch) or 2 large cookie sheets with parchment paper or a silpat liner and set aside. Cut butter into 1 tablespoon pieces.
CHOCOLATE BASE: In a medium pot over low heat, mix butter, milk, sugars, salt, and cocoa. Maintain low heat to prevent graininess. It'll be tempting to increase the heat, but don't! Stir often with a spatula, ensuring butter melts fully and scraping the pot's sides.
BOIL CHOCOLATE BASE: After the butter melts, raise the heat to medium. Stir until the mixture reaches a full boil, then continuously stir for one minute. Avoid under or over-boiling. Aim for 230°F if using a candy thermometer. Once done, remove from heat and stir briefly for 10 seconds.
FINISH COOKIES:Add peanut butter, stirring until smooth. Mix in vanilla, then oats, ensuring even coating.
LET COOKIES SET UP: Using a 2-tablespoon scoop, place cookie mixture on the sheet. Let cool until hardened, about 30 minutes or faster in the fridge.
STORAGE: These cookies taste great cold from the fridge and last up to 2 weeks in an airtight container there, or 1 week at room temperature. To freeze, set cookies on a pan in the freezer until firm, then store in a freezer bag with parchment layers for up to 6 months.
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Notes
Note 1: Unsweetened cocoa powder: Be sure to use unsweetened cocoa powder, not Dutch-processed cocoa powder.Note 2: Creamy peanut butter: Use creamy, not crunchy, peanut butter for best results. We love and highly recommend Skippy® Creamy Peanut Butter (not sponsored) in these cookies. If you use a no-stir (natural) peanut butter be sure it is well mixed before measuring for this recipe.Note 3: Oats: Most no bake cookies recipes call for quick oats, which work fine in this recipe. However, we are hooked on using old-fashioned oats instead! You can't beat the chewiness and additional texture these oats provide. Use whatever you prefer.