As usual, give us your best guess by commenting below. I'll let you know if you're right!
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Did you figure it out? It was boiled leg of mutton according to one of those in attendance, Mr. Wingate from the state of New Hampshire. It was held at the presidential mansion in New York City. At http://www.foodtimeline.org/presidents.html you can read a little more. I also found some interesting information about George Washington and his eating habits at this link http://blogs.smithsonianmag.com/food/2011/02/dining-with-george-washington/. Be sure to check out Martha Washington's cookbook.