Cooking recipe for twice as long - what temperature should I use?

[oopslateagain]

I have to go out unexpectedly, so need to put dinner on for about twice as long as usual.

It's thin sliced potatoes layered with bacon and onions, with a milk/flour/cheese mixture poured over. (I'm sure it has a posh name really )

I usually do it at 190C in my fan oven for about an hour, covered with foil for the first 40 mins or so.

I'll pop it in about 7:15, we won't be home until around 9 or so.

Can you not set the oven to start cooking at a certain time?

I'd put it in at about 165/170 covered with foil. Just remove the foil for a few minutes and pop it under the grill to brown the top when you get home

My (unscientific approach) would be to stick the oven on as you go out with the dish inside covered with foil. Oven to get up to 150 eventually. If it was a bit anaemic-looking when I got home, I'd take foil off and stick under the grill for 5-10 mins.

Sounds delish!

OneSwan I inherited the oven with no instructions and I can't figure the timer out!

Dauphinoise potatoes?