Heat 1/2 tsp oil in a pot on a medium heat. Add onion and cook for 1–2 minutes, until starting to soften.
Add parsnips, leek and 1/2 tsp salt to the pot and season well with freshly cracked black pepper. Cook for 3–4 minutes, then add stock and bay leaves. Bring to the boil, then reduce heat to low and cook for about 15 minutes, until veggies are tender.
Remove bay leaves from soup and use a stick mixer to blend soup, then fold through sour cream and lemon juice, until combined. Season to taste.