For the Jerusalem artichoke puree with fried Jerusalem artichoke slices, peel the Jerusalem artichoke tubers. Cut about a quarter of them into not too narrow slices and put them in some water with half of the lemon juice. Roughly slice the rest and also put it in water with the remaining lemon juice. Peel the onion and cut it into rings.
Heat the butter in a pot and sauté the onion until translucent. Drain the Jerusalem artichoke pieces, add them and sweat them while stirring. Add the vegetable broth and 2/3 of the whipping cream.
Cook the Jerusalem artichokes for 20-25 minutes with the lid on, then continue cooking without the lid until the liquid has almost boiled away. Season with salt, puree and keep warm.
Drain and dry the Jerusalem artichoke slices. Heat oil in a pot, fry Jerusalem artichoke slices in it for about 3 minutes until golden brown, drain on paper towels.
Whip the remaining whipped cream until stiff and fold into the puree. Loosely mix in the fried slices.
Serve the Jerusalem artichoke puree with the fried Jerusalem artichoke slices as a garnish.