Salted Texas Chocolate Sheet Cake

Preparation

1. Cake

   Step 1

   Preheat oven to 350°. Butter and flour a 13x9" baking dish. Bring cocoa powder, 1 cup butter, and 1 cup water to a boil in a small saucepan; remove from heat.

   Step 2

   Meanwhile, whisk sugar, baking soda, salt, and 2 cups flour in a medium bowl. Make a well in the center. Add eggs, buttermilk, and vanilla to well. Blend with a fork, then gradually incorporate dry ingredients. Add butter mixture and whisk until smooth. Scrape batter into prepared baking dish and smooth top.

   Step 3

   Bake until cake starts to pull away from edges of dish and a tester inserted into the center comes out clean, 35–40 minutes. Transfer pan to a wire rack.

2. Frosting

   Step 4

   Just before cake has finished baking, heat butter, milk, and cocoa powder in a medium saucepan over low heat, whisking occasionally, until butter is melted and mixture is smooth (do not let boil). Remove from heat and whisk in powdered sugar and vanilla.

   Step 5

   Pour warm frosting over warm cake and spread out and smooth with an offset spatula. Top with pistachios and sea salt.

   Step 6

   Serve slightly warm or room temperature.