Restaurants in book this writer makes up (7)
I believe the answer is:
bistros
'restaurants' is the definition.
(bistro is a kind of restaurant)
'book this writer makes up' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'this writer' becomes 'I' (the person writing the crossword).
'makes' becomes 'sorts' (I've seen this in another clue).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'sorts' in reverse letter order is 'stros'.
'b'+'i'+'stros'='BISTROS'
'in' acts as a link.
(Other definitions for bistros that I've seen before include "Small restaurants" , "Dread" , "Informal restaurants" , "Bars" , "places to eat..." .)