The MidWinter Feast is a celebration mainly for witches, however it is also celebrated by some residents of the Castle. It is a big occasion, and occurs during winter, hence the name.
According to Galen, being invited to a Wendron Witch MidWinter Feast is an honor, and should not be turned down lightly. The witches drink Witches' Brew and eat roast wolverine, stewed rabbit, baked squirrel, and a variety of sweet and spicy foods, which they barter for with Northern Traders and save specifically for the Feast. The Wendron Witches wear specific MidWinter Feast robes made of red fur. They gather around a fire to eat and drink, and the celebration carries on well into the night.
Aunt Zelda has a far more relaxed MidWinter Feast, eating stewed cabbage, braised eel, and spicy onions, then relaxing after dinner.