Besides using potions, how else do you recover HP? How do yo

Good question.

In the E3 demo there are only potions to aid you in getting health. That would not exclude from having food in the game that gives you health back. The latest podcast also mention this. If there is food in the game, it would be a nice surprise to actually see what we might expect (donuts and MacNcheezze).

Igavania have also some armor and weapons that might drain enemies or just give you health according to the rules given to the items. Perhaps we will also see drinking wine (I think there is are will be animation of Miriam drinking and tossing a glass of wine to the ground as a tribute to Iga) or find shards (sub-weapon power ups) that gives you some kind of health back.

Edit: Potions can be found in secret areas. Like walls, crates, lamps and enemies. The secret objects that can be broken to reveal potions might not be easy to find though and are hidden very well. Some have found 5 secrets in the E3 demo, I just found 3, all of them by accident.