- Preheat and prepare the pan:
Preheat the oven to 350°F (175°C). Line a 10×15 inch baking pan with parchment paper allowing a slight overhang for easy removal.
For a thicker cake, use a 9×13 inch pan; note that baking time may increase by 4–8 minutes. Lightly grease pan sides. - Combine dry ingredients:
In a large bowl, whisk together 2 cups granulated sugar and 2 cups self-rising flour until evenly blended. - Prepare the cocoa-butter liquid:
In a medium saucepan over medium heat, combine 1 cup unsalted butter, 1 cup hot coffee or hot water and 1/3 cup unsweetened cocoa powder.
Stir until the butter melts and the mixture comes to a gentle boil. Remove from heat once combined. - Incorporate hot liquid:
Pour the warm cocoa-butter mixture into the bowl with dry ingredients. Stir briskly for about 30 seconds to combine and slightly cool the mixture. - Add buttermilk and eggs:
Stir in 1/2 cup buttermilk and 2 room-temperature eggs until the batter is smooth. Avoid overmixing; mix only until combined. - Bake:
Transfer the batter to the prepared pan and smooth the top. Bake 20–25 minutes, or until the center springs back lightly and a toothpick inserted into the center comes out with a few moist crumbs. - Make the frosting:
While the cake bakes, prepare the frosting. In a small saucepan over medium heat, combine 1/4 cup butter, 1/4 cup buttermilk and 3 tablespoons unsweetened cocoa. Bring to a soft boil while stirring constantly. Remove from heat and whisk in 2 1/2 cups powdered sugar gradually until you obtain a smooth, pourable frosting. - Assemble:
When the cake is hot from the oven, pour the warm frosting evenly over the surface. Immediately sprinkle with toasted chopped pecans and semi-sweet chocolate chips. Finish with a generous drizzle of caramel sauce. If desired, scatter a small pinch of fine sea salt to balance sweetness. - Cool and serve:
Allow the sheetcake to cool until the frosting sets, about 30 minutes, then slice into squares and serve. For best texture, let the cake rest 1 hour so the layers settle and flavors meld.
