Preheat the oven to 350°F. Line a 9×9 baking dish with parchment paper. Be sure to allow for enough parchment paper to overhang the sides of the pan. This allows easy removal of the Snickers cake to frost, cut, and serve. Set aside.: The room fills with a warm, baking scent as the oven comes up to 350°F, an aroma that primes you for comfort baking. Lining the pan with parchment that overhangs is a tactile trick I never skip, because it makes lifting the whole cake effortless and keeps the sides from sticking. You should hear the faint hum of the oven and see a steady dial climb to the target temperature, which ensures even rise and consistent crumb. If your parchment slips, lightly grease the pan first to hold it in place, otherwise the batter can pool unevenly. A common mistake is not preheating fully, which leads to an uneven initial bake and a denser bottom layer.
In a large mixing bowl, stir together the packet of Devil’s food cake mix, 1/2 cup evaporated milk, melted & cooled butter, and the egg just until all ingredients are combined. The batter will be very thick.: As you stir, notice the batter change from powdery to dense and glossy, a sign the liquids are evenly incorporated. The scent will be cocoa forward and richer than a standard cake batter due to the melted butter . Mixing just until combined avoids overworking the structure, which would yield a tougher crumb. If the batter feels too dry, check your measurements because boxed mixes vary slightly, and resist the urge to overmix in an attempt to smooth it out. A common error is overbeating, which introduces air and can alter the dense texture you want.
Gently press half of the cake batter into the bottom of the parchment-lined pan. You may need to lightly wet your fingertips with cool water to help press the mixture into the pan. Bake for 15 minutes.: Pressing the batter gives a compact base that will support the caramel and toppings. The sensation is sticky but controlled; wetting fingertips helps you spread without tearing the parchment. During the first bake you should see the edges set and a slight sheen become matte, an indicator the layer is ready for its caramel topping. If you press too thinly, the layer can overbake and dry out, so aim for an even, modest thickness. Avoid using warm fingers to press, or the batter may smear unevenly.
While the cake is baking, you will need to place your unwrapped soft caramel candies and evaporated milk into a medium saucepan, on medium-low heat, for 6 to 8 minutes or just until all the caramel candies are melted, and the sauce is smooth. Turn off the heat to the saucepan and allow the caramel sauce to cool slightly while the cake finishes its first bake.: As the caramels melt you will smell deep, buttery notes and see a glossy amber sauce form, swirling slowly like warm honey. Stirring gently prevents scorching, and using medium low heat keeps the texture silky rather than grainy. When the sauce is smooth and fluid, take the pan off the heat and watch it settle, which prevents burning and helps it thicken slightly for better layering. A typical mistake is cranking the heat which will scorch the caramel and make it grainy, so keep the flame low and patient.
Top the warm cake with semi-sweet chocolate chips, 1/2 cup chopped peanuts, and caramel sauce.: Placing the semi sweet chocolate chips onto the warm layer allows them to soften without fully melting, creating little pockets of melty chocolate later. The chopped blanched peanuts add immediate contrast with their dry, toasted scent against the flowing caramel . Drizzling the warm caramel creates glossy ribbons that sink slightly into the warm cake, an effect that yields concentrated flavor spots. If you pour too much hot caramel, it may soak the layer excessively, so aim for a generous but controlled amount. Avoid distributing ingredients unevenly, as that will create inconsistent bites across slices.
Drop large spoonfuls of the remaining batter over the top of the caramel. Using a spoon, or damp fingertips, just lightly try to spread the batter. This batter will spread as it bakes, so you do not have to be precise when spreading the batter over the top. You really just want to make sure that most of the surface area has batter on it before the final bake.: When you dot the batter across the caramel, you will see it sit like islands, some merging during baking into a cohesive top. The tactile act of gently smoothing with damp fingers feels like painting, and it avoids tearing the parchment. This approach allows the caramel to peek through in places, creating visual contrast and flavor pockets. Resist the temptation to scrape the pan clean, because creating gaps is part of the appeal. A mistake here is over smoothing, which can eliminate the desirable pockets of caramel and nuts.
Return to the oven and bake for an additional 15 to 20 minutes or just until the top layer of cake is baked.: During this final bake the kitchen fills with a richer cocoa and toasted nut aroma as the top layer firms and the chocolate chips soften. Watch for the top to set, with edges pulling slightly from the parchment and a toothpick coming out mostly clean with a few moist crumbs. The visual cue is a golden sheen where the batter has cooked through, and you may hear a faint crackle as the surface finishes. Overbaking will dry the cake and mute the caramel pockets, so err on the shorter end of the time window and check early. A common misstep is assuming the center is done when the edges look ready, so always test the center gently.
Remove the cake from the oven and allow it to cool completely on the counter before removing the cake from the pan, using the overhanging parchment paper to help pull the cake out of the pan. Frost the cake with the tub of milk chocolate frosting, and garnish it with a drizzle of bottled caramel sauce and additional 1/4 cup chopped peanuts before slicing and serving.: Cooling fully lets the caramel set and prevents the frosting from sliding, and the cake will give off a faint nutty aroma as it returns to room temperature. Using the parchment overhang to lift the cake is satisfying and keeps the edges intact. When you spread the milk chocolate frosting , it will glide smoothly and create a glossy finish that contrasts with the matte cake surface. The final drizzle of bottled caramel and extra chopped peanuts add shine and crunch that entice the first slice. A typical error is frosting too soon, which melts the frosting and makes slicing messy, so cool the cake thoroughly before topping.