Belgian friends of my aunt passed on the meat stewed in dark beer with onions method, and that became a family favourite since my childhood. I still cook it.
A friend from Brussels who spent a month at our place many years ago also cooked us a dish with spinach, potatoes and lardons, which he claimed was a classic. It was also pretty good.
A current colleague of mine treated us to waffles last december (when the various teams at work at to host in turn a breakfast for all the others). He had the flour, a special type of sugar and the waffle iron sent from home for this. It was really good. He made another Belgian pastry, but I forget what it was.