The cake goes into the preheated oven for 18-22 minutes. It’s done when a toothpick inserted into the center comes out clean or with just a few moist crumbs. The smell as it bakes is intoxicating—chocolate and caramel filling the kitchen. The key here is to not overbake. Because it’s a thin cake, it goes from perfectly moist to dry quickly. I start checking right at 18 minutes. While the cake bakes, I quickly wipe out my saucepan to make the famous fudge frosting.
The frosting comes together in a flash. In the same saucepan, I melt the ½ cup of butter with the ¼ cup of cocoa powder and the ⅓ cup of milk, whisking until smooth and hot. I remove it from the heat and immediately whisk in the sifted powdered sugar and vanilla until it’s smooth and pourable. It should be like a thick gravy. The moment the cake comes out of the oven, I pour this warm frosting all over the hot cake, spreading it quickly to the edges with a spatula. It will start to set almost immediately. I immediately sprinkle the toasted chopped pecans evenly over the top, pressing them in gently so they stick as the frosting sets. Then, I walk away and let the whole glorious thing cool completely in the pan.
Pro Tips for Best Results
Timing is everything with the frosting. You must pour the warm frosting onto the hot cake straight from the oven. I’ve tried letting the cake cool first, and the frosting doesn’t soak in slightly or create that signature candy-like shell on top; it just sits on the surface and can be too thick. Pouring it on hot allows it to seep into the top layer of the cake, creating an irresistible fudge layer.
Toasting the pecans is a step I will never, ever skip. The first time I made this, I used raw pecans straight from the bag. The flavor was flat and almost waxy compared to the deep, rich cake. Toasting them unlocks their oils and gives them a robust, nutty crunch that stands up to the chocolate and caramel. It takes five minutes and elevates the entire dessert from great to sublime.
When swirling in the caramel, be gentle and don’t over-mix. You want distinct ribbons and pockets of caramel, not a homogenous tan batter. I make about 5-6 big dollops and run my knife through in a simple zigzag pattern just a few times. Over-swirling will cause the caramel to sink to the bottom and potentially make the cake stick.
Common Mistakes to Avoid
The most common mistake is using the wrong size pan. A 9×13-inch pan is too small. The batter will be too deep, the center won’t bake properly, and you’ll lose the classic thin, moist texture of a sheet cake. I made this error once and ended up with a gummy center and overcooked edges. A 10×15-inch jelly roll pan is essential for the right bake.
Don’t overbake the cake. Because it’s thin, it bakes quickly. Set a timer for 18 minutes and check it. It’s done when the edges just start to pull away from the pan and the center springs back lightly to the touch. A toothpick test is your best friend. Overbaking for even a few minutes can result in a dry cake, as the frosting won’t be able to compensate.(See the next page below to continue…)