A cold urn transformed into a hot pot (8)
I believe the answer is:
cauldron
'a hot pot' is the definition.
'cauldron' can be an answer for 'pot' (cauldron is a kind of pot). I am not sure about the 'a hot' bit.
'a cold urn transformed' is the wordplay.
'transformed' indicates anagramming the letters.
'a'+'cold'+'urn'='acoldurn'
'acoldurn' anagrammed gives 'CAULDRON'.
'into' is the link.
Can you help me to learn more?
(Other definitions for cauldron that I've seen before include "Very large metal pot for boiling" , "Witch's brewing pot" , "A large deep pot for boiling things" , "Witches' vessel" , "Very large pot used for boiling" .)