Texas Sheet Cake (Kopie)

*****
When time is tight and you need to throw something together for a picnic
or a potluck or a bake sale, this is the perfect crowd pleaser. It’s a large,
thin layer of tender chocolate cake slathered with gooey chocolate frosting
and sprinkled with toasted nuts. The frosting gets poured onto the cake
when they are both still warm. Some say "don’t mess with Texas," but this
cake can easily be spiced up by adding a teaspoon of cinnamon to the dry
ingredients or by swapping coffee for the hot water.

CAKE
1 cup (8 ounces) unsalted butter
1/2 cup (13/4 ounces) lightly packed premium unsweetened natural cocoa
3 tablespoons canola oil
1 cup water
2 cups (10 ounces) all-purpose flour
2 cups (14 ounces) sugar
1 teaspoon baking soda
1/2 teaspoon fine sea salt
2 eggs
1/2 cup buttermilk
2 teaspoons pure vanilla extract

FROSTING
1/2 cup (4 ounces) unsalted butter
1/4 cup (1 ounce) lightly packed premium unsweetened cocoa, preferably Dutchprocessed
1/3 cup whole milk
2 teaspoons pure vanilla extract
3 cups (12 ounces) sifted confectioners’ sugar
1/2 cup (2 1/8 ounces) toasted chopped nuts (such as walnuts, pecans, or hazelnuts; see Toasting Nuts, page 114)

Center an oven rack and preheat the oven to 375F.
To make the cake, melt the butter in a large saucepan over medium heat. Whisk in the cocoa. Add the oil and water and bring to a rolling boil for 30 seconds. Remove the pan from the heat and set it aside to cool slightly. Meanwhile, sift together the flour, sugar, baking soda, and salt in a large bowl, then whisk the ingredients by hand to ensure they are well mixed. Pour the warm cocoa mixture into the sifted ingredients and whisk until just combined. In a small bowl, whisk together the eggs, buttermilk, and vanilla. With a rubber spatula, stir the buttermilk mixture into the batter. Pour the batter into the greased pan and place in the center of the oven. Bake until the top is firm and a wooden skewer inserted in the middle of the cake comes out with moist
crumbs, 32 to 35 minutes.
While the cake is in the oven, make the frosting: melt the butter in a saucepan over medium heat. Whisk in the cocoa and bring the mixture to a rolling boil; boil for 30 seconds. Remove from heat and whisk in the milk and vanilla. Add the confectioners’ sugar 1 cup at a time while whisking continuously. Immediately after the cake comes out of the oven, pour the frosting over the hot cake and sprinkle with the nuts. Try not to jiggle the cake before it sets or you’ll leave waves in the frosting. Allow to cool before cutting into squares.
Well wrapped and stored at room temperature, this cake keeps for up to 5 days.