Didn't want to mess with oil, etc. late on a Saturday evening, but wanted to use up those Vidalias so I found this on a very interesting website: www.cookingforengineers.com. It made great onion rings!
This recipe is based on the Cook's Illustrated recipe from their Cover and Bake cookbook. As with all their recipes it is the best. But mine is better :)
Like all casseroles this one freezes well once prepared to just before you put it in the oven.