I know you’re joking, but the only way I can see it taking that long is if you put whole onions into an oven set to 180° to 200° F.
In a frying pan, one can easily caramelize an entire large frying pan of onions in about 30 minutes, or even faster if you decide to use physics to your advantage, and add a small amount of water to your pan and caramelize your pan of onions within 14 minutes. This is an advanced technique that requires some experience to try to use. Much like making a Dark Roux in 15 minutes.
put whole onions into an oven set to 180° to 200° F.
Wait, would that work?
Might need it to be a bit higher than that, but I know one can caramelize onions slowly in an oven. Just not sure what temp is needed
I’m absolutely not joking. If you’re cooking it for less than 45 minutes, you’re not caramelizing the onions. Frequent stirring, adding water, whatever, you can get the color and texture of caramelization, but not the flavor.
I spent a couple of years making slightly disappointing meals because I was focused on the color and texture of my onions instead of the flavor. When I finally took the time to fully caramelize them again, I remembered what I had been missing.
Try it and taste the difference if you don’t believe me.