Up-front warning: This pie is apparently not for everyone. I've loved the flavor of apples and horseradish together since I was in junior high, when I experienced a totally sublime horseradish applesauce served warm as a side dish in a German restaurant.
For about the last year, I've been developing this recipe for an apple horseradish pie, and it's at the point where I think it's ready. So I entered it in an apple pie baking contest, and it came in 6th place out of 7. The judges didn't like it. But a lot of people told me on the side that they tasted it and they really liked it a lot. A polarizing recipe, I guess... you're either going to love it or hate it. :-) Several people, after tasting it, have described it to me as, "a pretty normal apple pie, but with an unusual spice combination that you don't expect."
The tricky thing about the horseradish in this recipe is that you REALLY can't use a prepared horseradish from the store. Prepared horseradish is made with vinegar, and one of the first things I learned in my experiements is that the vinegar is out of place in an apple pie. Instead, you should prepare your own horseradish, and use lemon juice instead of vinegar. Then it works in apple pie. My kids really love this recipe, so I think it's good enough to post now. Hopefully it will keep being improved over the years!