other than specific dishes i imagine he might focus on soups/stews that can be served to multiple ppl unless there's extra hands during down time to peel potatoes for him or even the mages helping out or so
I used to work as a prep cook in a professional kitchen that did catering events, and you'd be surprised how much work a single skilled cook can do by themselves given time.
I mean, a lot of it has to do with having good knife skills and a robust knife bag, and planning out how you're going to do the work so you're not repeating yourself; for example, I can peel 5 pounds of potatoes or break down a chicken in about 3 minutes. I can do all the prep for a 40 gallon pot of vegetable broth in about 10 minutes, not including the time it takes to boil water, and if the vegetables aren't strained out, it's a pretty solid soup; granted, it has to be cooked for 8 hours to develop flavors, but prep time for things like soups and stews isn't really that high.
The reason I suggested he'd need a sous chef is for variety; a single chef can do one big dish really easily, but if the chef wants to do multiple courses or different dishes to accommodate dietary restrictions, that needs way more time.