*Update* I checked on the onions which were singed black on one side so took them out and ran under water and put them back in, they're purple onions.
I was going to put a tray of water at the bottom of the oven but want to see how whether this way can be done without burning and will do the water tray next time and compare.
I have had roast vegetables in the past and one evening decide to try to do them for myself. An utter disaster. They still seemed raw ages later. I slung them. If the whole onion thing works I might give roast veg another try.
Maybe it's the sealing them in olive oil for 3 days that does it.
When I tried I cut mine up, shoved them on the tray, drizzled oil over them, and roast/baked them for ages. Well more than 40 minutes. Still seemed hard & raw when I gave up and tried them.
Maybe I'll try again when I can face another disaster.
Old Geezer.........you need a HOT oven to roast veg....what was yours set at?
Also ...it depends how crammed in you have got them.......and how small the chunks!
Whenever I do roasted veg I always leave the onions in their skins. I quater them, drizzle with olive oil, salt and fresh thyme. I usually roast for about 45mins. Yes the skin goes black but you don't eat it anyway
I didn't take notes but feel sure it would have been on the highest setting. Can't look it up from here, but I'd guess about 210 to 220°C ish. About 1" chunks I'd say.
Black in 45 minutes ? I wish. Maybe my oven lies to me, perhaps I need a thermometer that survives inside to test it.