Shepherd's Pie in Advance
Is it possible to prepare and assemble a shepherd's pie (cook the filling, cook the potatoes, assemble to the point of final baking), refrigerate overnight, and bake off the next day? Would I want to bring it up to room temperature first (I'm guessing not), and if not, how much extra time in the oven might I need to give it?
Would I be better off preparing it completely and then just reheating?
I generally make mine in advance and them bake from the fridge at 350 for one hour before serving. For me, the point of a casserole is being able to make it when you have the time and then heat to serve at a later time.
Commercially frozen ones are popular in the UK, Canada, and even US stores like Trader Joes. And I have warmed leftovers without problem.
You could do it either way -- you'd have better results if you prepare it and then bake it the day you'll be eating it...
...but if you bake it ahead of time, you can always portion it out and reheat it as leftovers if the day goes completely upside-down.
I'm in the make ahead, over night even, bake when I'm ready camp. I usually remove it from the frig for a half hour before baking, to take the chill off; this will speed up the baking a bit.
As far as extra time in the oven if you bake it right from the frig, you'll have to check it. Bubbling and a nicely browned crust should mean it's ready. If in doubt, an instant read thermometer will give you an indication of the temperature in the center.