I think it's this, but I'm not sure: Almost from the earliest moments of our acquaintance I have come to feel for you a passionate admiration and regard, which despite my struggles has overcome every rational objection, and I beg you, most fervently, to relieve my suffering and consent to be my wife.

Mr. Darcy always thought Elizabeth was beautiful, commenting on her eyes repeatedly, but Elizabeth explains later on, that Mr. Darcy was most likely attracted to her because she was not trying to impress him, as all the other women were constantly doing. Her liveliness and unique way of interacting with him, she said, is what really caused his attraction. In the beginning of Chapter 60, Mr. Darcy does admit that he admired Elizabeth due to her "liveliness of mind"