Adjust rack to middle position and heat broiler or toaster oven. Break the crackers in half to form squares and place on a baking sheet. Arrange 4 marshmallow halves on top of each square. Broil for 30 to 60 seconds or until the marshmallows are golden brown. Break each chocolate bar into 12 pieces. Arrange the chocolate and raspberries on top of half the crackers. Invert the remaining marshmallow-topped crackers onto the raspberry-and-chocolate-topped crackers, pressing gently to make sandwiches. Stack them, if desired.