Cut them into slices as thin as possible. It’s easiest to use a mandoline, but if you're particularly skilled with your chef's knife, that can work too.
Next, place the slices in a bowl with ice-cold water and lemon juice. Let them sit for about an hour.
Then, transfer the slices to a clean cloth and pat them until they’re dry.
Pour the oil into your deep fryer and heat it to 180°C (356°F).
When the oil is hot, add the Jerusalem artichoke slices. Fry only a small portion at a time to prevent the oil temperature from dropping too much. They only need a couple of minutes, so keep an eye on them. They're nearly done when they start to wrinkle slightly.
Place the slices on a piece of paper towel or a clean cloth and pat them to remove excess oil. Sprinkle salt on them and let them rest for a few minutes before serving to ensure they get really crispy.