Butterscotch is a curious thing, none the least for the name.
We can all agree that its essential elements are butter and sugar, but the etymology of "butterscotch" itself? That's a different matter. One theory has it that "scotch" is a derivative of "scorched," a description of the slightly violent way the butter and sugar bubble together on the stove. Another argument is that "scotching" refers to scoring a butterscotch candy before it hardens, so you can break it apart more easily.
These are all well and good, but when I want butterscotch, I want butter and Scotch. Or Scotch-like booze at the very least. Butterscotch tastes best to me with a shot or two of the hard stuff for balance.
A butterscotch sauce or candy made with whiskey has an added depth and intensity, a bite beyond the uncomplicated sweetness of brown sugar and butter alone. It doesn't overtake the butterscotch's essential flavor, but it does make it more nuanced—something welcome in all kinds of desserts, but ice cream especially.
Truth be told, I don't use pricey Scotch in my butterscotch. A smooth, more affordable Irish whiskey like Jameson works just as well. But I don't skimp on the salt; fat and sugar can dull other flavors, and the chill of ice cream dulls them even more, so to get the most out of this sweet and salty treat, add salt with a heavy hand. (Because I also feel that yes, butterscotch should have a salty edge.)
Typical butterscotch is made with brown sugar, which these days is really just refined sugar with molasses added. The resulting taste is slightly acidic and harsh, even when rounded out by all that butter. Instead, consider using raw sugar, often labeled as "Sugar in the Raw" or "turbinado." It's partially refined, but much more true to sugar cane's flavor than molasses, and it makes for a more interesting, delicate butterscotch than brown sugar does.
If all this sounds like too much tinkering with the familiar, ask yourself, when's the last time you really enjoyed butterscotch? That you craved it like salted caramel? This recipe may swap around some ingredients, but it doesn't change the essentials of great butterscotch. It merely makes a dessert you'll want to eat tonight, with a second helping.