Here is my simple recipe that anyone can make with the things you have at home.
Set the oven to 350F and then in a bowl combine the ingredients as they are listed and make sure that they are mixed well between each ingredient. When well combined, grease a 8×13 pan. and poor the batter in. Bake it for 30 min. While the cake is baking make the the icing.
In a bowl add the ingredients as they are listed until you get to the powdered sugar. Just keep adding the powdered sugar until the consistency is pretty thick. You might need more or less depending on how big your egg was.
Let your cake cool somewhat before applying the icing. Sprinkles can be added for fun.