Halibut Olympia is a good thing, also...
350F oven is about right.
I use yogurt, sour cream, and mayonaise interchangeably and often mix equal amounts of any combo of the three.
In a glass baking dish lay down a layer of sliced onion rings.
Cover with the Y-SC-M as above and place the fish on top.
Cover with another layer of onion rings and then the Y-SC-M you like.
Cover with shredded cheese of your choice and cover with foil.
Bake for 10 minutes per inch of the total depth in the pan, uncovering the last 15-20 minutes to melt the cheese and brown it a bit.
Set aside for at least ten minutes after taking out of the oven to let the moisture redistribute.
Some like croutons either under or over the cheese...
