Hello! This recipe looks delicious. I would like to know what if any parts of this recipe can be done ahead of time, such as the night before. T...

Sorry, I hadn't read the recipe closely enough. I thought it was a re-make of the classic using ready-made onion rings. I think you could refrigerate the casserole with the fried shallots on top at the same time. If you don't have time to do the fried shallots, yes, of course you can cheat and use ready-made onion rings. I'd put those on top just before the casserole goes into the oven.

You could make the casserole 24-36 hours in advance, keep it refrigerated. Be sure to let it sit at room temperature for at least an hour to get the chill off before putting it in the oven. Ideally, put the onion rings on top just before you put the casserole into the oven - that will keep the onion rings crispier.