We're talking the shell and the filling. The inside's got to be liquid enough to whet and wet the cripsy outside, and the outside's got to be crisp and firm enough to support the gooey, liquid centre.
It's a balancing act to make Casanova's secretary look on with an expression of quiet jealous awe. Get it wrong and you're in trouble. Send your top five fillings to firstname.lastname@example.org