number one tip, always use natural lighting for food photography. That has to be one of my most valuable keys to successful photos. 2nd, you need a combo of a good camera and a great lens. I don't know of a course, I wish I did. There are a lot of videos on youtube. I think Tony Northrup puts out some good content, but in photography in general, not just food.
I hope your Christmas was amazing and I am so sorry it took me 4 days to respond.