“My mother made these for us 45 years ago, my children love them

Add Wet Ingredients & Sugar: Add the 2 large eggs, 2 large egg yolks, and 2 teaspoons vanilla extract to the chocolate mixture. Continue to whisk until the mixture is smooth and homogeneous. Whisk in the 2 ½ cups sugar until it is fully incorporated into the batter.
Incorporate Dry Ingredients: Add the 1 ¾ cups unbleached all-purpose flour and 3/4 teaspoon table salt to the bowl. Mix with a rubber spatula until just combined. Be careful not to overmix once the flour is added.
Assemble & Layer: Transfer approximately half of the brownie batter to the prepared pan. Using a rubber spatula, carefully spread the batter into the corners of the pan and smooth the surface. Sprinkle 3/4 of the coarsely chopped “fun-size” Snickers evenly over this first layer of batter. Carefully spread the remaining brownie batter over the Snickers layer. Sprinkle the remaining chopped Snickers over the top of the second batter layer.
Bake: Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs attached. The edges should be set, but the center should still look a little fudgy.
Cool & Serve: Transfer the hot pan to a wire rack and let the brownies cool in the pan for 1 ½ hours. Using the parchment overhangs, carefully lift the cooled brownies from the pan and transfer them to the wire rack. Let them cool completely on the rack for about 1 more hour. This complete cooling allows them to set fully and makes for cleaner cuts. Once completely cool, cut the brownies into 2-inch squares and serve.