I want to be unusual but do have to take some unadventurous palettes under consideration.
I only had Roasted Cream of Chestnut soup a few times but I think its holiday worthy.
kohlrabi served in a salad...batonnets or discs - unusual, but easy to accommodate to first time eaters - crisp, fresh, nice.
I'm totally in love with this soup: https://food52.com/recipes... It could fit your definition of "mysterious" because you can't tell what it is by looking at it. Is it carrot? Sweet potato? It's also pretty light and sweet-tart. Even my husband likes it, and he's about the pickiest person I know.
This soup is surprisingly good and simple to make - I would recommend starting with less mustard and brine then adding to taste, but otherwise following the recipe and allowing the toast to just start to burn: http://www.washingtonpost...
A creamy, buttery cauliflower puree looks like mashed or pureed potatoes: http://www.foodandwine...
How about a roasted parsnip soup with cardamom
Parsnip soup is a genius idea. Or try pureed parsnips, or celery root.