Whisk dry ingredients together. In a medium-sized saucepan, whisk together sugar, cocoa powder, flour and salt.
Add the milk. Pour in the milk and whisk until the lumps are gone.
Let simmer and thicken. Set the burner to medium heat and stir constantly for seven to ten minutes, or until the sauce has thickened into a gravy-like consistency.
Finish the gravy. After removing the pot from the heat, stir butter and vanilla into the mixture until the butter is completely melted and incorporated.
Pour over biscuits!
