Haven't made this yet, but I would guess a brownie recipe might make it better than box cake recipe... Less "cakey" , hold together better.
These were pretty good cookies. The cookie part is a soft cake-like chewy cookie which I liked, but the melted chocolate didn't really set so they were kind of messy to eat. And although we very much enjoyed these cookies, they didn't really taste like Girl Scout mint cookies (not the Thin Mints, anyway). But we enjoyed them nonetheless. Thanks, SaffronMeSilly. Made for 2009 Fall Pick-A-Chef.