Complex sentence: Originally, Drea de Matteo was cast as a restaurant hostess in the previous episode for that episode only, but creator David Chase liked her performance so much he developed the role of Adriana starting with this episode.
Split into simpler sentences: Originally, Drea de Matteo was cast as a restaurant hostess in the previous episode. She was only going to appear in that episode only, but creator David Chase liked her performance so much he developed the role of Adriana starting with this episode.