In a large pot over medium heat, melt 2 tablespoons unsalted butter and sauté 3 leeks and 1 chopped medium onion until softened, about 5 minutes.

Add 3 peeled and diced medium potatoes and cook, stirring frequently, for 5 minutes over medium heat.

Pour in 4 cups vegetable broth and bring the mixture to a boil over high heat.

Reduce heat to low, cover the pot, and simmer for 20 minutes or until the potatoes are tender.

Carefully transfer the soup to a blender or use an immersion blender to blend until smooth and silky.

Return the blended soup to the pot and stir in 1 cup heavy cream until fully incorporated.

Season the soup with salt and pepper to taste, stirring gently.

Refrigerate the soup for at least 2 hours before serving. Garnish with finely chopped chives and serve chilled.