I tried several and wasn’t happy with the flavor. So I made my own.
2 tablespoons butter
8 tablespoons milk
4 tablespoons cocoa powder (unsweetened, not cocoa mix, I used Green & Black organic)
8 tablespoons white sugar
Splash of vanilla extract
In small bowl, stir cocoa and sugar together, set aside. In saucepan over medium heat, melt butter. Whisk in milk, then whisk in cocoa/sugar. Keep whisking so no lumps form. Bring to bubbling boil for 1-3 minutes, continuing to whisk. Remove from heat, and continue to whisk for about 30 more seconds, then whisk in vanilla. It will thicken more as it cools.
Thick, glossy, and way better than anything available ready made. Less than 10 minutes.