For the relish, cut tomatoes into fine strips. Wash parsley, shake dry and chop. Wash the lemon hot, dry and finely grate the peel. Squeeze the lemon. Mix the tomatoes, parsley, olives, 4 tbsp. oil, 4 tbsp. lemon juice and zest.
Season to taste with salt and pepper.
Clean and wash the cauliflower and cut it into 6 slices (approx. 2 cm thick). Cut the rest of the cauliflower into small florets. Heat 1-2 tablespoons of oil in a large pan one after the other. Carefully fry the cauliflower slices in it in portions at low heat on each side for about 7 minutes.
Season with salt and some nutmeg, keep warm.
In the meantime peel and finely dice the onion. Peel, wash and chop the potatoes. Heat 1 tablespoon of oil in a wide saucepan. Fry the cauliflower florets, onion and potatoes in it. Pour 400 ml water on it, bring to the boil.
Cover and simmer for about 15 minutes. Grate the parmesan. Coarsely mash the potato mixture. Stir in cheese and crème fraîche. Season sauce with salt and pepper. Serve with cauliflower steaks and relish.