Shovel Knight: Treasure Trove

I was getting very annoyed with this one because I ran all over the tower talking to all the bosses while they wandered around. Finally I noticed that there is usually a different boss sitting at the banquet table each time you return to the tower from a level.

So just load a level then quit back to the tower. Go to the banquet table upstairs and talk to whichever boss is sitting at it. Load a level again and quit back to the tower. Return to the banquet table and speak with the next boss. Rinse and repeat to speak wirh all of them. The guys roaming around do not count, even when the boss characters are walking by. You don't have to load different levels. The same one over and over will work.

Hope this prevents someone from getting frustrated like I was.

Edit - Per SaucyCooper, you likely have to talk to all the roaming minions that are walking around AS WELL as each of the recruits (the ones that take turns at the table) to unlock this.