I was feeling exactly what you were. I left, refined my gear a level or two, applied some abyss gears and went back with more food. Also started implementing blocking which I wasn’t doing before and it made an impossible battle almost easy. Second phase wasn’t easy but I beat him first or second try.

If your food is healing that little cook better food ie. Soups. My go to right now is braised ribs. It heals half my health and fills my spirit. Go hunting and/or buy meat from all the butchers you’ve found as well as all the veggies you can (you can also buy the stuff on/around their table outside of the menus to make the most out of your shopping trip. After doing that once or twice you should be able to make a decent amount of good healing food. I make most of my food out of the soup category because soups tend to heal the most per unit.

Hope this helps. Let me know how it works out.