Extremely hot organist needs to get jiggy (8)

I believe the answer is:

roasting

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'extremely hot' is the definition.
'roasting' can be an answer for 'hot' (thesaurus). I'm not certain of the 'extremely' bit.

'organist needs to get jiggy' is the wordplay.
'organist' anagrams to 'ROASTING'.
However, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for roasting that I've seen before include "Lots of criticism" , "lecture" , "Criticising" , "Very hot" , "Cooking; severe criticism" .)

I've seen this clue in The Independent.

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