(I was thinking that I could make it up to the point of adding the cheese)

Yes, steps 1 & 2 could be executed in advance. I would hold off adding the lemon juice.

My guess is that this would freeze satisfactorily since it is basically just wilted cabbage and leeks.

If freezing one option would be to cook it to 85-90% of the desired consistency, then finish it off when you reheat the defrosted mixture.

That’s great Nancy. Thanks so much!

Yes, it will work made ahead.