Anneke

Water, because you can see what is happening. In a cool flat the main risk is rot and in water you spot a mushy base early instead of finding out in March. Small amount of water, bottom end down, changed weekly. Soil has less rot risk in some setups but you are working blind.

You can, it just takes longer and rot is much more likely, which is the only real reason the guides say spring. Roots grow when the plant has energy spare, and in a cool dim flat it has less of it, so the cutting sits there wet for longer with less going on.

First thing regardless of method: cut the leaf into sections a few inches long, keep track of which end was the bottom, and leave the cut ends to dry and callus for a day or two before they touch anything.