The first time I made this, the cookie dough didn't cook very well, so it was really gooey. The second time around, I cooked the cookie base first for a little while before adding the other ingredients on top of it. Also, the first time I made it, I made little discs of dough for the top, but the second time I just kind of crumbled it. I also doubled it for a 9x13.
Recipe from here.