Clean the leeks thoroughly to remove any dirt.
Slice the leeks and chop the onion.
In a large pot, heat the olive oil over medium heat.
Add the chopped onion and leeks to the pot and cook until softened.
Stir in the diced potatoes and cook for an additional 2 minutes.
Pour in the broth, bring to a boil, then reduce to a simmer for 20 minutes.
Blend the soup until smooth using an immersion blender.
Stir in the heavy cream and season with salt and pepper.
Simmer for another 5 minutes to heat through.
Serve hot, garnished with fresh herbs.