Grease a 9x13 baking pan and preheat oven to 350. Combine all cake ingredients and mix with a stand or hand mixer for 2 minutes. Pour cake batter into prepared pan and bake for 45 minutes or until set and a toothpick comes out clean. Move pan to a cooling rack to cool.

Prepare frosting by melting butter and stirring in cocoa. Add the powdered sugar, milk, and salt to the cocoa and butter mixture and mix until smooth. If necessary, add more milk a little at a time until you reach your desired consistency. Once cake is fully cooled, spread frosting evenly over cake and serve. If not serving immediately, refrigerate until ready to serve.