Could you make sauerkraut with spinach? I'm just wondering if you can ferment spinach in a similar way you can ferment cabbage leaves? Would this have appealing results at all?
Something I've never tried, however, my immediate thought is the comparison of cooked cabbage to cooked spinach.

I imagine nothing more than a jar full of green-black slime.

I'd love to hear what happens if you try, though ;)