i haven't made this in awhile, but i do remember that it took much longer to cook then the recipe suggested and it was really soft....kinda like you said. but when the toothpick comes out clean....then i remove, let cool, and cover in saran wrap and place in freezer overnight. it is a really soft....almost like a soft fudge texture....not really a cake texture. it will firm up overnight w/o any problems.
i hope this helps! let me know if you have anymore questions!