Beat the margarine, sugar and eggs in an electric mixer or by hand.
Sift and mix the flour, cornstarch and chocolate.
Gradually add the dough and milk to the mixture in the mixer and mix with a whisk or a spoon until smooth.
Add the yeast and mix gently.
Put it in a greased shape and take it to the oven preheated to 180 degrees for approximately 40 minutes or until you stick a toothpick and it comes out clean.
Note: You can replace the chocolate with chocolate, but you have to reduce the sugar so the cake doesn't get too sweet.
ROOF:
Place all the ingredients in a non-stick pan or thick aluminum pan, bring to a low heat and stir constantly, when boiling, leave it on the fire until it thickens.
When you take it off the fire wait a little and put it on top of the cake.