In a two quart microwave bowl:
Put 1/2 cup cocoa
1/2 cup cornstarch
1 1/2 cups sugar
1 cup milk
Stir well then add 3 cups more milk
Microwave for 6 minutes then stir. Microwave an additional 4 minutes and it should be thickened. If not...continue with 2 minute increments until it is.
We use an 1100 watt microwave. That is why I posted the additional increments...in case yours is less.
You can close your eyes to the things you do not want to see, but you can't close your heart to the things you do not want to feel.