Earthy molasses is an ideal partner for naturally sugary sweet potatoes while spicy jalapeo and mustard add balance. When you toss the sweet potatoes, make sure to reserve the molasses mixtureyoull drizzle that over the sweet potatoes once theyre roasted. Stone-ground mustard refers to the method of using a stone to pulverize mustard seeds. But, if you cant find it, a sharp mustard like dijon will work, too.