The most christmassy christmas dish in Danish tradition is "Risengrød" (Literally rice-porridge). It's a warm porridge made from almost exclusively rice and full-fat milk. The porridge is served with a scoop of butter as well as ground cinnamon and sugar on top. It might sound boring but it's actually a savory dish which fills you up with 'hygge'.

Throughout December we usually have risengrød for dinner once or twice. And each time my mother would set aside one bowl. She'd prepare it with butter and cinnamon and everything and together we'd go upstairs and climb up the ladder to the attic. We'd put the bowl on the floor right next to the stairs and go back down. 
The next morning I'd run upstairs to find the bowl empty with dried-in porridge and cinnamon scraped up the edges. I loved feeding the Nisse.