Carmelized onions

[Saregama]

Previous thread - probably worth combining.

Caramelizing onions in the oven?

I just became a convert to pierogies filled with cheese and potato from my local supermarket. I want to caramelize a bunch on onions, but I honestly don’t want to stand over the stove and keep stirring. Neither do I want to use the slow oooker. I have a nice cast iron pot, and I plan to cut up three pounds of onions, and cook them in butter in the oven. Do you have any idea about temperature and timing? I want to do low and slow so I don’t have to babysit with lots of stirring.