TreeTapper2, I agree, the first maple runs are often very buttery tasting. I've made 5 batches of soft/sugar maple syrup so far this year and all have been buttery. This, however, is definitely different. It's deeper and richer and the butterscotch flavour is very pronounced.

If you've got some box elders and your season isn't over yet, you should give it a try. Even if it's one mini-batch! You could just boil a gallon on the stove like I did as an experiment.