Cast or frame walls in the basement? Also question about windows

[Robert Nyberg]

Hello!
Apologies if this ended up in the wrong category.
We have a slightly unusual situation in our basement. The entire basement has been excavated afterwards and the issue here is that the new foundation wall, which supports the old one, is about 10cm inside the old one (see image).

The initial thought was just to frame with steel studs and insulate behind. But to save space in this room, the ultimate solution would be to align the lower wall with the upper one and then plaster it.

It should be mentioned that the foundation is insulated with 200mm Isodrän.

How would you solve this in the best way?

Bonus question: We also plan to make an opening in the wall straight ahead for a window (12x5). Above the foundation wall rests a longitudinal floor beam (see image), what considerations should I have regarding load-bearing here?

Thanks in advance!
/happy amateur

 

[Rabbithole]

Lay a layer of leca or lightweight concrete and then smooth it out?

 

[Robert Nyberg]

Build a layer of leca or lightweight concrete and then plaster it smooth?

That was actually the only solution I could think of myself too, which is probably the best/only option then

I was wondering if there was some other super-duper trick that you more experienced folks knew.

So that's what it will be! Thank you