Julienne cut the onion and sauté in butter. Clean the spinach, wash it and add to the onion. Sauté the spinach until limp without covering, add the thinly sliced potatoes, a pinch of salt and lastly the freshly grated Parmigiano Reggiano cheese.
Cook for a few minutes and add enough water to cover the ingredients. Leave to boil for 15 minutes, then mix the ingredients in a blender. Add the milk cream and mix. Serve the spinach soup and decorate the dish with Parmigiano Reggiano cheese petal-shaped slivers and a dash of Traditional Balsamic Vinegar.