In a large pot, heat olive oil over medium heat. Add the sliced leeks and sauté until softened, about 5 minutes.

Stir in the diced potatoes and cauliflower florets; cook for another 3 minutes.

Pour in the vegetable broth, bringing it to a boil. Reduce heat and simmer uncovered until vegetables are tender, approximately 15-20 minutes.

Remove from heat and let cool slightly. Blend the mixture until smooth using an immersion blender or countertop blender.

Return the blended soup to low heat and stir in the heavy cream gradually. Season with salt and pepper as needed.

Serve hot, garnished with fresh herbs.