I found this recipe on the website, Smitten Kitchen, and have found it to be an absolute favourite with any chocoholic! I have adjusted it slightly, but not too much.
The sauce will thicken as it begins to cool, so you might want to wait for 15 to 20 minutes off the heat before serving.
Any leftovers can be poured into a jar and stored in the refrigerator for up to a month. Then when you need a quick chocolate fix, simply scoop out a little (or a lot) and reheat in the microwave.
Adapted from the recipe at https://smittenkitchen.com/2017/06/best-hot-fudge-sauce/