At first it may seem easy to make that igloo cake or a cake shaped like a half-moon: the only difference between baking a dome shaped cake and baking the traditional two layer confection is pouring the cake batter into the roundest oven-safe mixing bowl you possess. But that doesn't take into account the fact that a differently shaped container comprised, most likely, of a different material than a cake pan and filled with a higher volume of batter just won't cook the same way. Still, the idea of a dome cake is not at all impossible, so long as you know the proper procedure.
Preheat your oven to 25 degrees F less than the temperature indicated on your specific cake batter recipe. Choose a glass, oven-safe mixing bowl. Pyrex glass works well for this.
Spray the surface of the bowl with cooking spray.
Pour the batter into the mixing bowl as if it were a baking pan.
Place the bowl in the oven. Five minutes after the amount of time specified in your cake batter recipe, test the center of the cake with a toothpick. When the toothpick comes out clean, the cake is done. The center will not likely be fully cooked at this point due to the shape of the bowl. Keep the oven on and check on the cake every five minutes until it is done.
Invert the bowl to remove the cake after baking.
You can always use a specialized dome cake pan instead. Consider carving off cake to create a more circular look. If you want multiple layers, simply cut them into the cake with a large bread knife.
Gingerly insert a rubber spatula to free a sticking cake from the mixing bowl after baking.