Man stood up by Agnes, perhaps, in the Italian restaurant (7)
I believe the answer is:
lasagne
'the italian restaurant' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'man stood up by agnes perhaps' is the wordplay.
'man' becomes 'al' ().
'stood up' says the letters should be written backwards (in a down clue, letters go up).
'by' means one lot of letters go next to another.
'perhaps' is an anagram indicator.
'al' reversed gives 'la'.
'agnes' anagrammed gives 'sagne'.
'la'+'sagne'='LASAGNE'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for lasagne that I've seen before include "Form of pasta" , "Baked pasta dish" , "Flat sheets of pasta" , "Italian cooking" , "Italian dish with layers of pasts and mince between" .)