I found a great recipe on cooks.com.
1 C white sugar
2 T flour
1/3 C cocoa
2 T butter
1 C milk
I added a drizzle of vanilla
Stir in a saucepan until everything is hot and creamy. Bring to a low boil. Stir constantly. Boil until desired thickness. Sauce will continue to thicken when it cools.
This made LOTS of sauce. I am putting some away in the fridge for another night!