As a little kid, I was always told that a Hamantasch is representative of Haman's three cornered hat. Is there an actual source that says Haman wore a three cornered hat or is it just Folklore?
I was told the following by a Rebbe of mine (My Yiddish is sorely lacking, so can't verify it to be true, but why would he make this up?):
In Europe, they made "hamantaschen" out of poppy, which in Yiddish is Mon. A pocket in Yiddish is a Tasch. Mon-Tasch, or plural Mon-taschen, (poppy pockets) were a popular purim snack. The similarity of Mon to Haman caused people to start calling it that, and afterwards the "explanation" came along.
A possible connection with Haman's hat is that the Ibn Ezra Writes that Haman had affixed his idol to his hat. When people bowed to Haman they also bowed to the idol on the hat.
Eating something with a connection maybe symbolizes destroying the idol on the hat. This is just a theory.