Crab concoction by one of the family that's a real gem (9)

I believe the answer is:

carbuncle

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

'real gem' is the definition.
'carbuncle' can be an answer for 'gem' (carbuncle is a kind of gem). I'm not sure about the 'real' bit.

'crab concoction by one of the family' is the wordplay.
'concoction' indicates an anagram.
'by' says to put letters next to each other.
'one of the family' becomes 'uncle'.
'crab' anagrammed gives 'carb'.
'carb'+'uncle'='CARBUNCLE'

'that's a' acts as a link.

Can you help me to learn more?

(Other definitions for carbuncle that I've seen before include "Cluster of boils - jewel" , "Bright red gem; boil" , "Large boil-like inflammation - gemstone" , "Sort of boil; a gem" , "eyesore architecturally" .)

I've seen this clue in the Evening Standard.

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