This is the recipe I used for Max's dinosaur cake at his dino party. It's much more rich and dense than a cake from a box. I like to top with with buttercream frosting, because you can color it for kids' cakes, and there's so much chocolate in the cake, that it doesn't need chocolate icing, although there's no such thing as too much chocolate...
2 1/4 c all purpose flour
2 t baking soda
1/2 t salt
1/2 c butter
2 1/2 c packed brown sugar
2 t vanilla extract
8 oz. unsweetened baking chocolate, melted
1 c sour cream
1 c boiling water
Preheat oven to 350 degrees.
Sift together flour, baking soda, and salt, and set aside.
In a large bowl, combine butter and brown sugar, and mix until smooth. Add the eggs, one at a time, and continue to mix. Then beat in the vanilla extract and melted chocolate. Add in 1/2 the sour cream and 1/2 the dry ingredients, and blend well. Then add the rest of the sour cream and dry ingredients and boiling water, and mix together until consistent.
Bake in a greased 9x13 pan for 35 minutes, or until a toothpick inserted into the center comes out clean.
Wait until it has cooled completely to decorate. If you have time, bake it a day early, so that the chocolate flavor has time to fully develop.
This is my take on a recipe I found, here.
Image courtesy of Stuart Miles / FreeDigitalPhotos.net