Scally oddly dealing with sauce (5,8)
I believe the answer is:
salad dressing
'sauce' is the definition.
(salad dressing is a kind of sauce)
'scally oddly dealing with' is the wordplay.
'oddly' indicates alternate letters.
'dealing with' becomes 'addressing' ('address' can be a synonym of 'deal with').
The alternating letters of 'scally' are 'sal'.
'sal'+'addressing'='SALAD-DRESSING'
(Other definitions for salad dressing that I've seen before include "Mayonnaise, e.g." , "sauce" , "Eg, Thousand Island or French" , "what goes on rocket?" , "saucy thing!" .)