Sauce pot chocolate cake

Sauce pot chocolate cake 

3 oz baking chocolate 

1 c brown sugar (packed) or white sugar.

1 T molasses optional

3 eggs (large)

½ c coffee, water or milk

2 T butter

2 t vanilla extract

2 c cake flour

2 t cream of tartar

¾ c milk

1 t baking soda dissolved in ¼ c of warm water

Prepare a 13x9 inch cake pan by lining with wax paper.

Place oven rack to the center.

Preheat oven to 350º

1. Melt chocolate, sugar, coffee in a 3 qt saucepan.
2. Beat eggs and add chocolate mixture. Return to heat and cook until it is like a custard sauce. Continually stir and watch carefully.
3. Remove pan from heat, stir in butter and vanilla and let cool. I put the pan in a larger pan of cold water. It can take 30 min or more to cool (body temp) without a water bath. 
4. Mix flour, cream of tartar and milk (¾ c) into the chocolate and beat until smooth.
5. When the oven is ready, pour the baking soda water into the batter and stir. You'll see bubbles and it will get lighter and increase in volume. Use a spatula to make sure all the batter is mixed through.
6. Pour batter in pan and bake on the middle rack for about 40 minutes.