Follow these steps carefully, especially the boiling time, as it is the most critical part of ensuring your no-bake cookies set up perfectly every single time.

1. Preparation is Key: Before you begin, prepare your “landing zone” for the cookies. Line two large baking sheets with parchment paper or wax paper. This step is essential for preventing the cookies from sticking and ensures effortless removal and cleanup. Have all your ingredients measured and ready to go, as the process moves quickly once you start cooking.
2. Create the Sugar Syrup: In a medium-sized, heavy-bottomed saucepan, combine the unsalted butter, whole milk, granulated sugar, and packed light brown sugar. Place the saucepan over medium heat. Stir the mixture constantly with a wooden spoon or heatproof spatula as the butter melts to ensure the sugar begins to dissolve and everything is well combined.
3. The Critical Boil: Continue to stir as you bring the mixture to a full, rolling boil. A rolling boil is one that cannot be stirred down. Once it reaches this stage, stop stirring and start a timer for exactly one minute (60 seconds). This is the most important step in the entire recipe. Boiling for less than a minute will result in cookies that are too wet and may not set. Boiling for longer than a minute will evaporate too much liquid, resulting in cookies that are dry and crumbly.
4. Remove from Heat and Add Flavor: As soon as the one-minute timer goes off, immediately remove the saucepan from the heat. Place it on a heat-proof surface. Stir in the pure vanilla extract, ground cinnamon, and salt. The mixture will be very hot, so be careful of any steam. Stir until these ingredients are fully incorporated.
5. Incorporate the Dry Ingredients: Add the old-fashioned rolled oats and the raisins to the hot sugar mixture in the saucepan. Use your spatula to stir everything together until the oats and raisins are evenly coated. You’ll need to work relatively quickly here, as the mixture will begin to thicken and set as it cools.
6. Scoop and Drop: Using a medium cookie scoop (about 1.5 to 2 tablespoons) or two spoons, drop rounded mounds of the cookie mixture onto your prepared baking sheets. Space them about an inch apart; they won’t spread like baked cookies, but this gives them room to set without touching.
7. Patience and Setting: Let the cookies sit at room temperature to cool and firm up completely. This process typically takes about 30 to 60 minutes. You will know they are ready when they are firm to the touch and can be easily lifted from the parchment paper without falling apart. Avoid placing them in the refrigerator to speed up the process, as this can sometimes affect the texture.
8. Serve and Store: Once the cookies are fully set, they are ready to be enjoyed. Store any leftovers in an airtight container at room temperature. They are best enjoyed within 3-4 days for optimal freshness and texture.