Crossword Genius

Increase penalty in the end following misery initially at a Shetland winter festival (2,5,2)

Ross

I believe the answer is:

up helly aa

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

'winter festival' is the definition.
(I've seen this before)

'increase penalty in the end following misery initially at a shetland' is the wordplay.
I cannot really see how this works, but
'increase' could be 'up' (upping is a kind of increasing) and 'up' is found within the answer.
'a' is within the answer.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

(Another definition for up helly aa that I've seen is " winter festival".)

I've seen this clue in The Guardian.
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