Lasagna layer (5)
(Other definitions for sauce that I've seen before include "Moistener for food" , "Dressing for food - cheek" , "Relish or impertinence" , "Cranberry or brandy, say" , "Cheek; condiment" .)
'lasagna layer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ricotta that I've seen before include "dairy produce" , "One soft cheese" , "may be served with biscuits" , "Sheep's milk cheese" , "Italian 4 across" .)