My copy of The Joys of Yiddish surfaced. Before it submerges (or i submerge), here is Leo Rosten’s answer to SL’s query:
Rosten defines “schmaltz” (for which he offers an alternative spelling, withouT the “c”) in three ways:
1. Cooking fat (mostly chicken)
2. “Corn”, pathos; maudlin or mawkish substance; excessive sentimentality; overly emotional mush; sugary banality.
3. Luxury; wealth; good luck. “He fell into a tub of shmaltz, that’s how lucky he is.”
No connection mentioned with “old country and old-fashioned, like Momma’s cooking” — certainly not in a Yiddish context. Rosten is, I think, highly regarded as an authority on Yiddish. Some may know him better as Leonard Q. Ross, the brilliant creator of H*Y*M*A*N K*A*P*L*A*N