When I was studying French in high school and college, I learned that Christmas Eve was la veille de Noël. Technically, I suppose, one can say that but I have seldom heard the term. My French friends talk about "le 24" or, more often, "le réveillon", sometimes specifying "le réveillon du 24" in order to distinguish this festivity from the "réveillon du 31." "Le réveillon" is an elaborate holiday evening meal, often served quite late -- after midnight mass for some.
My family celebrates Christmas "entre nous", so only my husband, my two daughters and I are involved in this celebratory supper. I used to put myself out making elaborate dishes, but over the past few years we have adopted "boudin blanc", a plump white sausauge filled with ground chicken, veal or pork mixed with egg, milk and soft bread crumbs. It is generally available in some shape or form all year round, but I make a point of buying it only for the holidays.
My Larousse Gastronomique lists 8 types of boudin blanc in its chart entitled "Characteristics of Different Boudins." The variety I buy from the local butcher, though, contains specks of morel mushrooms and is not mentioned in the Larousse.
Traditionally, boudin blanc is a starter, and it can even be considered a side dish, but for us it is the star of the Christmas Eve meal. I cook the sausages simply, wrapping them individually in aluminum foil and sticking them in a hot oven for 20 minutes. With steamed red potatoes and sautéed apples on the side, they make a quick and festive réveillon meal for a small group.