You can empty the supply on turn 1. http://forum.dominionstrategy.com/index.php?topic=17800.0
A: So, have you come across Dominion before?
B: I've heard of it. Let's give it a go.
A: Ok, I'll go through the rules quickly.... Now let's deal out a random kingdom.
B: Cool, I think I've got it. I'm sure it'll all make sense after a turn or two anyway, do you want to go first?
A: Let's see, what have we got in this kingdom, Villa, Fortress, Watchtower...
(few minutes later)
A: ...and the supply is empty so I'll stop there. Thanks for playing.
B: Don't mention it. What other games have you got?