Boxed cake mixes give you the latitude to increase moisture content to your tastes, as long as you stick close to the basic proportions of sugar, fat, flour and eggs. In fact, you can deviate by up to 20 percent in most cake recipes and increase moistness if you keep the basic formula the same. When you're using a boxed cake mix, you have even more wiggle room because, although they still follow the basic cake formula, they also have additives that make them difficult to mess up. Increase the moistness of any cake mix by changing the amounts and types of fats and dairy.

Heat the oven to 350 or 325 degrees Fahrenheit. Use 350 F if you're using a glass or metal pan, and 325 F if you're baking in a dark-metal pan. Grease the pan and dust it lightly with all-purpose flour.

Add the cake mix, 1 cup of full-fat dairy, 1/3 cup of oil and 1/3 cup of melted unsalted butter to a mixing bowl. Adding an extra 1/3 cup of fat increases the moisture without adding water, and using butter improves the mouthfeel while maintaining structure. Exchanging full-fat dairy for water increases the fat content and helps the cake retain more water.

Add 4 egg yolks to the mix instead of 3 whole eggs. Egg whites have desiccant properties, but they make excellent binders. Using about 1/3 as many more egg yolks, or 4 yolks instead of 3 whole eggs, as called for by the instructions on the box, and omitting the whites provides the binding needed without the associated drying.

Mix the cake using a hand mixer on Low for 30 seconds, then increase the speed to High and mix for 2 minutes. Pour the cake batter in the baking dish and place it in the oven.

Bake the cake 23 to 28 minutes when using a standard 13-inch-by-9-inch baking dish. Check the cake by inserting a toothpick in the center after 20 minutes of cooking.

Heat the oven to 350 or 325 degrees Fahrenheit. Use 350 F if you're baking in a glass pan and 325 F if you're baking in a dark-metal pan. Grease and flour the pan.

Add the cake mix, 1 box of instant pudding, 3 whole eggs and 1/3 cup oil to the mixing bowl. Instant pudding makes the cake denser without adding too much volume, partly because of the additives it contains, such as agar and lecithin. The instant pudding doesn't have to match the color and flavor of the cake to work.

Add 1 cup of full-fat sour cream or yogurt instead of water. Sour cream and yogurt increase the fat content of the cake and work with the pudding to add moisture and smoothness.

Mix the cake using a hand mixer on Low for 30 seconds, then increase the speed to High and mix for 2 minutes. Pour the cake batter in the baking dish and place it in the oven.

Bake the cake 23 to 28 minutes when using a standard 13-inch-by-9-inch baking dish. Check the cake by inserting a toothpick in the center after 20 minutes of baking.