Dairy Queen's Jack and Jill Sundae is a classic ice cream sundae with marshmallows added on top. In other words, a Jack and Jill sundae is simply a regular sundae with marshmallow topping. It's just a little twist to be sure, but little things can make all the difference.
A couple of brothers who supplied ice cream mix stopped by, and somebody poured a swirl of ice cream on paper, stuck a stick in it and dipped it into chocolate. “Somebody said that's really a dilly,” and the name stuck, Phyllis said in a 2010 oral history interview for StoryCorps.