This is my great-aunt Delia's famous New Year's Day main dish, with notes for a cheaper version that my mom made most Sundays. It is so good that my sibs and I would fight (literally) over the last bits of rice clinging to the pan! Don't be tempted to replace the butter with margarine--this is a holiday meal, after all, and you just don't skimp for holidays! Also, don't forget to dry the poultry. If you don't, the butter won't stick to the skin and help crisp and flavor it. Oh, and canned mushrooms work fine instead of fresh.