Given any date, I need to find the date of the previous Thanksgiving Day.

For example, if the date in cell A1 is 9/28/2009, then the date of the
previous Thanksgiving Day in cell B1 would be 11/27/2008. However, if the
date in cell A1 is 12/5/2009, then the date of the previous Thanksgiving Day
in cell B1 would obviously be 11/26/2009.

I know how to find the date of the current years Thanksgiving Day using
=FLOOR(DATE(YEAR(TODAY()),11,29),7)-2. But finding the previous Thanksgiving
Day has been elusive.

Any help would be greatly appreciated.

Thanks,
Bob