Peel the potatoes and celery root, and cut them into cubes.

Melt the butter so it's ready when the root vegetables are tender.

Boil them in unsalted water for about 15 minutes until they are very tender.

Drain the root vegetables and mash them coarsely while adding whole milk and butter to reach the desired consistency.

Season with salt, pepper, and lemon juice.

 

Peel the Jerusalem artichokes and pat them dry thoroughly.

Cut them into very thin slices using a mandolin slicer. Pat them dry again using a tea towel.

Pour the oil into a pot and heat it to about 180 degrees Celsius (356 degrees Fahrenheit).

Fry them until golden in small batches. Ensure you don't put too many in the pot at once, as the oil's temperature drops when adding them.

Briefly dab them with a tea towel or paper towel and sprinkle with a good salt.