Complex sentence: Susan's parents meet and have dinner with the Costanzas for the first time, where both families obsess over a loaf of marble rye bread that wasn't served with the meal, which Frank takes back home.
Split into simpler sentences: Susan's parents meet and have dinner with the Costanzas for the first time. The Costanzas bring a loaf of marble rye bread which, when it isn't served after the meal, Frank takes back home.