I always start by heating my oven to 350°F, or 325°F if I'm using a dark or nonstick pan. Then I line my 9-inch square pan with foil, letting extra hang over the edges so I can lift the brownies out later. A light coat of cooking spray on the foil keeps everything from sticking.
Next, I stir together the brownie mix with the eggs, oil, and water listed on the box instructions. I pour the batter into my prepared pan and spread it out evenly with a spatula. Baking usually takes around 45 minutes, but I always check a few minutes early with a toothpick.
Once baked, I let the brownies cool completely on a rack, which takes about an hour and a half. This step matters more than people think, since warm brownies will melt your frosting instantly. After cooling, I freeze the whole pan for about 15 minutes to firm it up before cutting.
Using the foil overhang, I lift the entire brownie slab out of the pan in one piece. I peel the foil away gently and set the block on a cutting board. Then I slice it into 16 even squares, working in 4 rows by 4 rows for consistent turkey bodies.
I spread a thin layer of chocolate frosting over the top of each brownie square, saving a couple of teaspoons aside. This frosting layer does double duty, adding flavor and acting as glue for the candies. I keep the layer light so it sets up fast in the fridge.
Here's the fun part I let my kids help with every time. I place one peppermint patty near a corner of each brownie, then use the reserved frosting to stick on two candy eyeballs and one orange candy half for the beak. Finally, I fan out a few pieces of candy corn behind the patty to form the tail feathers.