I'm calling this a staple and not a desert, because in my house this IS a staple.
This is based on a recipe from Amy Dacyczyn's book The Complete Tightwad Gazette. Her recipes are always the best.
I've changed it to be a bit easier to vary the quantity to get the amount you want.
I put the cocoa and sugar in a saucepan and then I add boiling water. Whisk together and heat to boiling (or microwave) until smooth. About 3 minutes. Add the salt and vanilla. You can also add other extracts (peppermint anyone?). I've occasionally short-changed this one and not boiled it long enough. That made it a little lumpy -- but it still tasted wonderful. Boiling just gives it that nice silky syrupy texture.
Let it cool and store it in the refrigerator. It is supposed to last 2 months, but mine never stays in the refrigerator for that long. I put it in a salad dressing bottle and we put it on top of most of our deserts. You can make chocolate milk or the best mochas.
Whatever measure you choose to make a "part" your end result will be about 3 times that amount.