Mix the flour, salt, and cinnamon in a medium bowl. In the bowl of your electric mixer, mix the warm water with the honey and yeast. Allow it to foam for 10 minutes. Then add the flour mix and the rest of the ingredients for the dough into the yeast mixture. Using a bread hook, knead the dough on low in the mixer, until you have a soft, smooth and elastic dough (about 8-10 minutes).
Put the dough in an oiled bowl. Cover tightly and let it rise for 2 hours or until it's puffy and nearly doubled in size.
Lightly butter a 9-inch round or oval baking pan that's at least 2 inches deep (or use a greased 9-inch springform pan.)
Toss the apple chunks with the sugar, cinnamon and rum. Gently deflate the dough. Transfer it to a lightly greased work surface, and flatten it into a rough rectangle, about 8x10 inches.
Spread half the apple chunks in the center of the dough. Fold a short edge of the dough over the apple in order to cover it, patting firmly to seal the apples and spread the dough a bit. Spread the remaining apple atop the folded dough. Cover the apples with the other side of the dough, again patting firmly (Basically, you've folded the dough like a letter, enclosing the apples inside.)
Take a long knife and cut the apple-filled dough into 16 pieces. Cut it in half, then each half in halves, etc... This will be very, VERY messy. The dough is slippery, apples will fall out, sugar syrup will ooze. It's not pretty. Don't worry about making all the pieces the same size.
Lay the dough chunks into the pan. Crowd them so that they all fit in a single tight layer. Lots of apple chunks will fall out during this process; just tuck them in among the dough pieces, or simply spread them on top.
Cover the challah gently with lightly greased plastic wrap or a damp towel and let it rise for about 1-2 hours, until it's a generous 3 inches high (it should come above the rim of the pan). Twenty minutes before the end of the rising time, preheat the oven to 325 degrees F.
Place the bread in the lower third of the oven. Bake it for 55 minutes, or until the top is at least golden brown all over and has no white spots.
Remove the challah from the oven, and after 5 minutes loosen the edges and carefully transfer it to a rack.
Cool completely. Then whisk together the cider and powdered sugar and brush or drizzle it over the top, allowing it to drizzle down the sides.