"Denver" Chocolate Sheet Cake

From the kitchen of One Perfect Bite...No, despite what you think, this is not a Texas sheet cake. It's a Denver chocolate sheet cake and the recipe for it first appeared in a Denver Junior League Cookbook. I found the recipe in The New York Times. In all fairness, no one is sure how Texas sheet cake got its name or where it originated. The issue is further confused because the cake is also known as buttermilk brownies, brownie sheet cake, chocolate brownie cake, chocolate sheet brownies, Mexican chocolate cake, Texas brownie cake, Texas cake, Texas sheath cake, and “plain old” chocolate sheet cake. I suspect Denver chocolate sheet cake could also be added to that list, though it has greater height than the Texas version. What all these cakes have in common, is the use of buttermilk and a frosting that contains nuts. The true Texas version is baked in a rimmed cookie sheet or jelly roll pan and makes a large cake that is barely an inch high. Its Denver cousin is higher by an inch. These cakes are all easy to make and are great to make when you have a crowd to feed. In the recipe below, you will see that the amount of cocoa is given as a range. The 1/4 cup version will produce a mildly flavored milk chocolate type cake. I doubled that amount for both the cake and frosting you see in the photos that accompany tonight's recipe. This recipe makes a moist sweet cake that I know you will enjoy. Here is how it's made.

Denver Chocolate Sheet Cake...from the kitchen of One Perfect Bite courtesy of the Denver Junior League via the New York Times

Ingredients:
Cake
16 tablespoons unsalted butter in 16 pieces (plus 1 tablespoon softened butter for greasing pan)
2-1/2 cups all-purpose flour (more for pan)
2 cups sugar
1 teaspoon baking soda
1/4 teaspoon salt
1/4 to 3/4 cup cocoa
1/2 cup buttermilk
2 eggs, lightly beaten
1 teaspoon vanilla
Frosting:
8 tablespoons unsalted butter in 8 pieces
1/4 to 3/4 cup cocoa
6 tablespoons buttermilk
1 teaspoon vanilla extract
1/4 teaspoon salt
1 pound confectioners' sugar
1/2 cup chopped walnuts or pecans

Directions:
1) To make cake: Place oven rack in middle position; heat oven to 350 degrees. Grease and flour a 9-by-13-inch sheet pan.
    Combine flour, sugar, baking soda and salt in a large bowl, and whisk well.
    Combine butter, cocoa and 1-1/2 cups water in a medium saucepan over medium-low heat; whisk frequently until butter has melted and mixture is smooth, glossy and bubbling around edges. Remove from heat.
    Fold cocoa mixture into dry ingredients until just combined.
Stir in buttermilk, eggs and vanilla until combined.
Turn batter into prepared pan and bake until cake has risen, shrunken slightly from edges, and tests clean with a toothpick, about 25 to 30 minutes. Remove from oven, and cool completely on a rack.
2) To make frosting: Combine butter, cocoa and buttermilk in a small saucepan over medium-low heat, whisking frequently until butter has melted and mixture is smooth and bubbling around edges. Remove from heat and transfer to a standing mixer bowl fitted with a paddle attachment.
    With machine on low speed, add vanilla, salt, sugar and nuts, and mix until smooth. (Ingredients may also be whisked into cocoa mixture by hand; if so, sugar should be sifted first.)
    Pour warm frosting over top of cake, and smooth with a spatula. Allow frosting to become firm before slicing cake.