In a small sauce pot, combine water, sugar, cocoa powder, and dark chocolate.
Place the sauce pot over medium-high heat and start whisking continuously.
Keep whisking until the mixture comes to a boil. Allow it to boil for about 10 seconds.
Remove the sauce pot from the heat immediately.
Your chocolate sauce is now ready to enjoy! You can serve it hot over ice cream or let it cool and then drizzle it over your favorite dessert.
Notes
For a thicker sauce, you can boil it for a minute or two, but remember to keep whisking the entire time to prevent sticking or burning.
Keep in mind that the sauce will naturally thicken as it cools down.