Crossword Genius

Cooks tell our mob in fancy parlour to make stew staple (10,8)

Ross

I believe the answer is:

portobello mushroom

I'm a little stuck... Click here to teach me more about this clue!

'cooks tell our mob in fancy parlour' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'to make stew staple' is the wordplay.
I cannot quite understand how this works, but
'to' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.
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