Texas Sheet Cake, At Last

Ingredients

• 2 cups (400 g) granulated sugar
• 2 cups minus 2 tablespoons (257 g) all-purpose flour
• 1 teaspoon baking soda
• ¾ teaspoon ground cinnamon (optional)
• ½ teaspoon fine sea salt
• ½ cup (120 ml) buttermilk, well shaken and at room temperature
• 2 large eggs, at room temperature
• 1 teaspoon pure vanilla extract
• 16 tablespoons (226 g) unsalted butter, cut into chunks
• Scant ½ cup (40 g) unsweetened cocoa powder
• 1 cup (240 ml) very hot water
• 2 teaspoons instant espresso powder (optional but recommended)
• 12 tablespoons (170 g) unsalted butter, cut into chunks, for the topping
• Scant ½ cup (40 g) unsweetened cocoa powder, for the topping
• ⅓ cup (80 ml) heavy cream
• 3 cups (360 g) confectioners’ sugar, sifted if lumpy
• ¾ cup (90 g) chopped toasted pecans

Instructions

1. Center a rack in the oven and preheat to 350°F (175°C). Butter a 13-by-18-inch rimmed sheet pan, dust it lightly with flour, and tap out the excess, or coat it thoroughly with baker’s spray.
2. Whisk the granulated sugar, flour, baking soda, optional cinnamon, and salt together in a large bowl. In a separate bowl or measuring cup, whisk the buttermilk, eggs, and vanilla until smooth.
3. Put the butter, cocoa powder, hot water, and optional espresso powder in a medium saucepan. Cook over medium heat, whisking often, until the butter melts and the mixture comes to a full boil.
4. Immediately pour the hot cocoa mixture over the dry ingredients and whisk until mostly combined. Add the buttermilk mixture and whisk just until the batter is smooth and evenly blended.
5. Pour the thin batter into the prepared sheet pan and spread it to the corners. Bake for 18 to 22 minutes, until the cake springs back lightly and a tester inserted in the center comes out clean.
6. While the cake bakes, make the topping. Combine the butter, cocoa powder, and heavy cream in a medium saucepan. Bring to a boil over medium heat, whisking, then remove from the heat.
7. Whisk the confectioners’ sugar into the hot cocoa mixture in several additions until the icing is smooth, glossy, and pourable. Keep it warm over very low heat if the cake is not yet ready.
8. As soon as the cake comes out of the oven, pour the hot icing over the hot cake. Spread it quickly and gently from edge to edge; a little icing will soak into the surface.
9. Immediately scatter the toasted pecans evenly over the icing. Let the cake cool completely in the pan until the icing sets, then cut into 15 generous squares.