The French knowledgeable about Northern dish (7)
I believe the answer is:
lasagne
'dish' is the definition.
(lasagne is a kind of dish)
'the french knowledgeable about northern' is the wordplay.
'the french' becomes 'la' (one of the French words for 'the').
'knowledgeable' becomes 'sage' (I can't explain this - if you can you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'sage' enclosing 'n' is 'sagne'.
'la'+'sagne'='LASAGNE'
Can you help me to learn more?
(Other definitions for lasagne that I've seen before include "Italian cooking" , "Fool ran as angel (anag) - pasta dish" , "Pasta served in strips" , "Flat sheets of pasta" , "Course" .)