Complex sentence: Because Thanksgiving is always on a Thursday, this meant that turkey and pumpkin pie, two Thanksgiving staples, were forbidden, not only for that holiday, but for Christmas and New Year's Day as well, since those holidays landed on Thursday in 1947.
Split into simpler sentences: Because Thanksgiving is always on a Thursday, this meant that turkey and pumpkin pie, two Thanksgiving staples, were forbidden. This was also the case for Christmas and New Year's Day since those holidays landed on Thursday in 1947.