Step 1: Line two large baking sheets with parchment paper or wax paper. Set aside.
Step 2: In a large heavy-bottomed saucepan, combine the granulated sugar, milk, unsalted butter, and unsweetened cocoa powder. Place over medium heat.
Step 3: Bring the mixture to a full, rolling boil, stirring constantly to prevent scorching. Once boiling rapidly, continue to boil for exactly 1 minute, stirring continuously. This step is crucial for the cookies to set properly.
Step 4: Immediately remove the saucepan from the heat. Stir in the vanilla extract until combined.
Step 5: Add the creamy peanut butter to the hot mixture. Stir vigorously until the peanut butter is completely melted and smoothly incorporated.
Step 6: Quickly add the old-fashioned rolled oats to the mixture. Stir well until all the oats are evenly coated with the chocolate-peanut butter mixture. Work swiftly as the mixture will begin to thicken as it cools.
Step 7: Using a tablespoon or a small cookie scoop, drop spoonfuls of the mixture onto the prepared parchment-lined baking sheets. You can gently flatten them slightly with the back of the spoon if desired.
Step 8: Allow the cookies to cool completely at room temperature for about 30-60 minutes, or place them in the refrigerator for 15-20 minutes to speed up the setting process. Once firm, they are ready to serve. Store any leftover no bake cookies recipe treats in an airtight container at room temperature or in the refrigerator.