Today is known as Verloren Maandag (Lost monday) where I live.
It used to be a Flemish tradition to eat appels covered in dough and sausage rolls (that is the best I can describe what you see on he pic). But now Lost Monday is a tradition almost exclusive to the Antwerp region of Belgium.
It takes place on the Monday after the Sunday in which Epiphany is celebrated (Three Kings or “Driekoningen“). So today we are all having one. Hmm...
Where does it come from? I was told, having worked in the Antwerp Harbour ,that traditionally, the harbor workers were allowed to drink while the natiebazen( the 'bosses' in the harbor, natie I guess you can sort of translate as a craft unions in the Middle ages) paid for it. They were offered something to eat with so they wouldn ´t get too drunk and this food was made of meat that they couldn´t sell and bread... And since the workers didn´t work that day... Lost Monday.