I really wanted to make this but it is a rare thing for me to have either cream or sour cream in my fridge. I do, however, always have Greek yoghurt!
I cooked four potatoes and tipped them in a dish with the cooked cauliflower where I mashed them together roughly, figuring lumpy bits would be OK in a rustic dish like this. I went to town with the grated nutmeg and pepper and then added the yoghurt, doubling the recommended amount so that the entire mix bound together.
With loads of beautiful parmesan on top, it went into the oven for about a half hour; just long enough for the top to get crunchy.
I think the yoghurt substitute was fabulous, adding a lovely tang to the dish, and will definitely do it again next time.