It was sweet seeing broken legs finally very firm internally (7)

'it was sweet' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'broken legs finally very firm internally' is the wordplay.
'broken' is an anagram indicator.
'finally' suggests the final letters.
'firm' becomes 'co' (abbreviation for company).
'internally' is an insertion indicator.
The last letter of 'very' is 'y'.
'legs'+'y'='legsy'
'legsy' is an anagram of 'glyse'.
'glyse' enclosing 'co' is 'GLYCOSE'.

'seeing' is the link.

Can you help me to learn more?