Hotpot! Dumplings! (Though, honestly, we eat that every other holiday as well or as soon as there are more than two at home who have the extra time on hands)
Dumpling roulette is definitely a winter holidays exclusive item, however. Hiding all those lemons, wasabi, peppers and coins. A surprise in every bite.
Skillet Fudge. My grandmother used to make it every year and no one has replicated the exact mix she made. We have the recipe but no one's gotten it to taste JUST like hers.
Hawaiian Toast - Basically cheese on toast with ham and pineapple. My gran got the recipe from a magazine about 60 years ago (back when pineapple was new and exciting in Britain) and we've been having it ever since for Christmas eve dinner.