Hottest maiden, one working in restaurant for useful experience (5,2,3,4)
I believe the answer is:
grist to the mill
'useful experience' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'hottest maiden one working in restaurant' is the wordplay.
'maiden' becomes 'm' (cricket abbreviation).
'one' becomes 'i' (roman numeral).
'working' indicates anagramming the letters.
'in' indicates putting letters inside.
'restaurant' becomes 'grill' (grill is a kind of restaurant).
'hottest'+'m'+'i'='hottestmi'
'hottestmi' anagrammed gives 'isttothem'.
'isttothem' placed inside 'grill' is 'GRIST TO THE MILL'.
'for' is the link.
Can you help me to learn more?
(Another definition for grist to the mill that I've seen is " source of profit?".)