Good rule to be broken for porridge (5)
I believe the answer is:
gruel
'porridge' is the definition.
(gruel is a kind of porridge)
'good rule to be broken' is the wordplay.
'good' becomes 'g' (abbreviation**).
'to be broken' is an anagram indicator.
'rule' is an anagram of 'ruel'.
'g'+'ruel'='GRUEL'
'for' is the link.
(Other definitions for gruel that I've seen before include "Unappetising food" , "Unappetising meal of boiled oatmeal" , "cheap fare" , "Thin porridge" , "disappointing fare" .)