How to make chocolate cake

Here's one from allrecipes.com, which is a very reliable recipe site. Below the recipe you'll find comments from people who have already tried it.

http://allrecipes.com/Recipe/Easy-Microw...

Easy Microwave Chocolate Cake
Submitted by: Laura
Rated: 3 out of 5 by 14 members Prep Time: 6 Minutes
Cook Time: 2 Minutes Ready In: 8 Minutes
Yields: 1 servings

"Whether you're craving chocolate cake at midnight or 3 PM, this made-in-minutes, fudgy microwave version will satisfy your chocolate passions. Just have a fork ready."
INGREDIENTS:
3 tablespoons butter, softened
1/4 cup white sugar
1 egg
1 teaspoon vanilla extract
1/4 cup milk
1/2 cup all-purpose flour
2 tablespoons cocoa powder
1/4 teaspoon baking powder
1 pinch salt

DIRECTIONS:
1. Spray a medium microwave-safe bowl with non-stick spray and set aside. In a mixing bowl, combine the butter, sugar, egg, vanilla extract, and milk; blend together. Combine the flour, cocoa powder, baking powder and salt; blend into the mixture until smooth. Pour into greased bowl.
2. Cover and cook in the microwave on high for 2 to 2 1/2 minutes, or until cake springs back when touched. Since all microwaves cook differently, adjust the cooking time to accommodate your machine. To serve, let the cake cool five minutes, then cover the bowl with a plate and turn both bowl and plate upside down so the cake falls onto the plate.


They have additional microwave cake recipes but this one appears to be the highest rated.