1-Prepare the hot chocolate mixture: In a saucepan, bring 1 cup (240 ml) water, 1 cup (227 g) butter, and 3 tablespoons (22.5 g) cocoa powder to a boil, stirring until smooth. Set aside to cool slightly.

2-Mix dry ingredients: In a large bowl, whisk together 2 cups (240 g) all-purpose flour, 2 cups (400 g) granulated sugar, 1 teaspoon (5 g) baking soda, and 1/2 teaspoon (2.5 g) salt.

3-Combine wet ingredients: In another bowl, mix 1/2 cup (120 g) sour cream, 2 large eggs, and 1 teaspoon (5 ml) vanilla extract until smooth.

4-Build the batter: Stir the sour cream mixture into the dry ingredients. Pour in the hot chocolate mixture and mix until you have a smooth, thin batter.

5-Bake the cake: Pour batter into the prepared 18×13-inch pan. Bake at 350°F (175°C) for 15-20 minutes, or until a toothpick comes out clean. The cake will be about 1 inch thick.

6-Make the frosting: While baking, boil 6 tablespoons (90 ml) milk, 3 tablespoons (22.5 g) cocoa powder, and 1/2 cup (115 g) butter. Remove from heat, stir in 3 3/4 cups (450 g) powdered sugar, and beat until lump-free.

7-Frost the cake: Pour hot frosting over the hot cake, spread evenly. Let set for 10 minutes before slicing.

8-Serve: Cool slightly and dig in. For adaptations, use dairy-free options.