Polymer clay can have a translucency to it that mimics food really well, and there are some special tricks you can do to get very realistic food.
I'd recommend youtube Miniatures tutorials by SugarCharmShop, as she does very clear simple tutorials with great results. Her stuff is dollhouse sized but if you do the same things slightly larger you can make treats and accessories for any size of doll.
Here's a link but it autoplays a video with sound so be aware of that.
(She also repaints vinyl dolls and does doll clothing tutorials you can probably use for your BJD.)
Here's her video of polymer clay basics. Here's one for her tools she uses.
Here's a second channel where she had a lot of the food videos and they're still there. Sound!
She's just a fantastic resource for anyone who loves dolls.
