Sweetens rolls, boundless pasta sauce (4)
I believe the answer is:
'pasta sauce' is the definition.
(I've seen this before)
'sweetens rolls boundless' is the wordplay.
'sweetens' becomes 'rag' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rolls' becomes 'clues' (cluing is a kind of rolling).
'boundless' indicates the central letters (the limits or bounds of the word are removed).
The centre of 'clues' is 'u'.
Can you help me to learn more?
(Other definitions for ragu that I've seen before include "pasta sauce" , "tomato and meat sauce" .)