You should be able to find it under "recent foods," click on it, and it will fill it in for you. Alternatively, you could just add the quantity you eat the next time to the entry that's already in your list, though some prefer to keep it as two separate entries.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days