Easy one-bowl chocolate cake. Recipe makes a dense, moist cake.
For the Cake. Preheat oven to 350 degrees F. Spray a 9x13-inch cake pan with nonstick cooking spray or grease with solid shortening and dust lightly with cocoa powder. (See note for round and cupcake baking instructions.)
In a large bowl, whisk together 2 cups flour, 2 cups granulated sugar, ¾ cup cocoa powder, 1 ½ teaspoons baking powder, 1 teaspoon salt, and ½ teaspoon baking soda. Add 3 large eggs, 1 cup water, and ½ cup oil. Whisk until smooth. Use a rubber spatula to scrape the bottom of the bowl and mix in any flour that was clinging to the bowl.
Pour batter into prepared pan. Bake until a cake tester inserted into the center of the cake comes out clean, about 35 minutes. Remove cake from oven. Cool 9x13-inch cake in pan.
For the Frosting. In a large bowl, beat 2 stick butter until light. Add the ⅓ cup cocoa powder and mix until combined. Stop the mixer. Add the 4 cups powdered sugar and 3 tablespoons milk. Mix on low speed. Increase speed to medium and beat until fluffy. If frosting is thick add an additional tablespoon milk.
Frost chocolate frosting or your favorite frosting.
For a round cake. Grease two 8 or 9-inch round cake pans with nonstick cooking spray or grease with solid shortening and dust with cocoa powder. Check cakes for doneness after 25 minutes. Allow cake to cool in the pan for about 10 minutes and then remove cake from oven and let cake cool completely on a wire rack.
For cupcakes. Line 24 muffin cups with paper liners. Fill cupcake cups about 2/3 full. Check for doneness after about 18 minutes. Allow cupcakes to cool in the pan for about 5 minutes and then remove cupcakes from pan. Cool completely on a wire rack.