Barb,

I meant to address my previous post about lazy pierogi casseroles to you, rather than Susan (mea culpa), since you were the person who asked about a dish you tried in a restaurant.

It seems to me that these pan-baked pierogi casseroles are probably subject to a lot of variation, since they themselves are a variant of the true, hand-formed pierogi pies. Could the mushroom sauce in the pierogi you tried have been a bechamel (milk-based white sauce) with mushrooms in it, or a veloute sauce (meat-broth-based white sauce) with mushrooms in it?

Also could it have been simply from a condensed mushroom soup out of a can, as is used in a lot of "lazy" casseroles?

I'd try these different possibilities and try to duplicate the one you had at the restaurant. Or maybe ask the restarant chef; some chefs are pretty obliging with recipe requests or, at least, some general ideas about how to make the dish at home.

Sandy