Defining a "muffin" is tricky. If it's essentially chocolate cake, sans frosting, does it really count as a muffin? But lacking frosting, you can't really call it a cupcake. Either way I love them.
Ingredients:
2c flour
1c sugar
3/4c choc chips
1/4c choc chips for topping
1/2c unsweetened cocoa powder
1 tsp baking soda
1 tsp vanilla
1 egg
1c plain yogurt
1/2c milk
1/2c veg oil
Combine flour, sugar, 3/4c chips, cocoa powder, baking soda in large bowl
Combine remaining ingredients in smaller bowl, whisk thoroughly
Pour liquid mixture into dry and mix until just blended
Pour into a dozen+ baking cups, sprinkle with remaining choc chips
Bake at 400 degrees for about 18 minutes