Heat content of the pan, largely empty, sadly (8)
I believe the answer is:
enthalpy
'heat content' is the definition.
('enthalpy' can be a synonym of 'heat content')
'the pan largely empty sadly' is the wordplay.
'empty' suggests removing the centre.
'sadly' indicates an anagram.
'largely' with its middle taken out is 'ly'.
'the'+'pan'+'ly'='thepanly'
'thepanly' with letters rearranged gives 'ENTHALPY'.
'of' is the link.
(Other definitions for enthalpy that I've seen before include "Thermodynamic measure of total heat content" , "Measure of energy" , "Thermodynamic quantity" , "Function for physical chemists" , "Total heat content of a system" .)