expanding, duplicating, or otherwise increasing quantity has nothing to do with transfigureation, transmorgification or polymorphing in any way, shape, or form.
it can simply be done by hyper-cellular mitosis (done by hightening and de-limiting the metabolisim. You can do this with a few bio-chemichals if you know what ones) however for meat this may require some degree of necromancy, assuming you are trying to grow an un-cooked steak. magiscience proves wizards are dicks every time.

if you want to go in to baked goods, that is far more complicated and might accually fall under gamp's law

(it's exceptions, atleast)

Fysics: law of conservation of matter.

The magic doesnt simply 'create' new matter, it modifies existing matter so that the molecular configuration is suited to the desire of the witch or wizard.

Also, inb4 IT IS MAGIC IT DOESN'T HAVE TO EXPLAIN SHIT. Yes, I considered that.

What you didn't consider was that you spelled Physics wrong.

You are correct. DAMNIT.