What temperature and time should I use for a cupcake recipe? I am having difficulty baking a vanilla and chocolate cup-size cake. The ingredients are as follows:

12 (1 ounce) squares semisweet chocolate, chopped
1 cup butter, cut into pieces
1 cup cold milk
1 1/4 cups all-purpose flour
1 pinch salt
2 eggs
1 teaspoon vanilla extract
1/4 cup white sugar

The problem is that the cake burns on the outside, and then the inside is not completely done. If I reduce the amount of batter I use in the tin to a half-size cup, they end up as cookies. I have also tried to reduce the temperature from 200 degree to 100 degree, extending the time from 15 minutes to 30 minutes but still do not get a well-balanced end result.

I would like to know if I have a bad mixture of ingredients, or a completely wrong temperature and timing for cupcakes.
Firstly, it strikes me as odd that your recipe has no raising agent - no baking powder, no bicarbonate/baking soda, no self-raising flour. Unless you're whipping a lot of air into the batter, the cakes will barely rise, and you will end up with 'cookies'.

I would add 2 teaspoons of baking powder and 1/4 teaspoon of bicarbonate of soda (baking soda) and see if that helps.

As for the temperature of your oven, I wouldn't go so far as to halve the temperature and double the time. The idea is that you need enough heat for the cakes to rise at a decent rate then form a crust on the outside. 100 degrees will do little but slowly dry the cakes out.

Domestic ovens are rarely well calibrated, so your oven may be running hotter than the dial indicates. Invest in an oven thermometer to make sure you are setting the temperature correctly: I have had an oven run 40 degrees hotter than the dial said before now!

If you haven't got the time to get a thermometer, try setting the oven about 20 degrees cooler on the dial, to around 180 degrees.