After the presents are opened and the stockings are turned inside out, Christmas Day can seem like one long spell of "some assembly required" until supper. So try hosting an open house, where friends can drop in during the afternoon, families can mix and mingle, kids can show off their new toys, and you don't need to cook a formal dinner. The central dish, a purchased ham, is a gift for the cook: All you have to do is unwrap it. And many of the remaining dishes can be made two days ahead. Blue cheese spread with crackers is a three-ingredient hors d'oeuvre; creamy cauliflower soup can be made ahead and reheated; and both herbed roasted sweet potatoes and frisée salad take just a few minutes and hold up well on the buffet table. A peppermint-topped cheesecake is a fun spin on a can't-miss dessert. All in all, it's a simple but satisfying meal ― with only some assembly required.