Peel onions and potatoes. Scrape parsley root. Chop onions. Dice potatoes and parsley. Slice leeks.

Heat oil in a large pot. Add onions, parsley, and potatoes. Stir-fry for 5 mins. on medium heat.

Add sliced leeks and fry for another 5 mins.

Pour stock and sprinkle thyme, salt, and pepper. Boil soup on low heat until potatoes are done (around 15 mins).

Pour half the soup in another pot. Blend with a hand blender and mix with unblended half of soup.

Serve.