1 cup of water
1 cup of sugar
3 tablespoons of vanilla
1 cup cocoa
In a small sauce pan whisk the water and cocoa under medium heat. From there add sugar and keep whisking. You need to check to see if its sweet enough for what you like, if its not sweet enough add more sugar. Continue to whisk, this isnt something you want to leave on the stove because it burns very easily, and yes I had to learn that the hard way lol. When this comes to a simmer take off the heat and whisk in the vanilla. Do not boil its very important you let this come to simmer but not to a boil. When its cool enough go ahead and put it the fridge it will thicken.
Its that easy and a lot less expensive than to buy it at the store. You could also serve this over ice cream too. However you use this sauce I hope this is useful for you. Live, laugh and love.