I acquired a leaf cutting from a beefsteak begonia several weeks ago from a friend. I didn't have time to do anything with it at that moment so I just dropped it in a cup of water until now. I just have a leaf with a long petiole, but there are now several long roots growing at the tip of the petiole where it was cut from the original plant.

I don't have much experience with this so I'm curious how to best proceed. At first I thought I could just put the petiole tip in soil, but I don't think there is anything from which a new plant to grow currently. I was reading that one method is to make slices at the leaf veins and put the leaf directly against moist soil. Is this the better method for my situation? Any specifics for a beefsteak begonia would be extremely helpful.