I had a sort of epiphany last week inspired by the presence of both ice cream and chocolate cake in my kitchen at the same time, but an absence of toppings.
Here's what happened next:
Dropped a overflowing tablespoon or so of liqueur into a bowl. (I used triple sec, but I think this should work equally interestingly with almost anything.)
Gently nuked it until it was hot enough to melt chocolate.
Dropped in a single square of the darkest chocolate I had on hand (in my case, the nicely priced 80% chocolate noir bars from Costco).
Stirred, melted, adjusted for consistency.
Results: die-for chocolate sundae sauce! So good, I decided right then I had to get the word out.
You might find you need to nuke a bit more if the chocolate doesn't melt the first time. Just be conservative, because the chocolate will start to re-congeal if it's heated too long.