Chilled Curried Potato-Leek Soup

This recipe is from Williams-Sonoma and is perfect of a hot summer night. It is chilled but thanks to the leeks and curry, this soup still packs a wallop flavor-wise. 

2 tablespoons unsalted butter
1 large yellow onion, chopped
3 leeks, white part and 1-inch of the green, halved lengthwise, carefully washed and sliced crosswise
1 clove of garlic, minced
1 1/2 tablespoons curry powder
3 cups vegetable broth
4 red potatoes, about 1 lb. total, thinly sliced
sea salt to taste
3 cups milk
freshly ground pepper to taste

1. In a large stock pot melt the butter over a medium heat.  Add the onions and leeks and saute, stirring until the vegetables begin to soften, about 5 minutes.  Add the garlic, and curry powder, stirring until the garlic is fragrant and the powder is fully absorbed.  Continue to saute the mixture stirring frequently until the vegetables are soft, about 10 minutes.  Add the vegetable stock, potatoes, and salt (as needed).  Cover and cook until the potatoes are soft when pierced with a fork, about 20 minutes. 
2. Remove the soup from the stove and add the milk.  Working in small batches, puree the soup in a blender or food processor.  As each batch is pureed transfer the soup to a large bowl.  Cover and chill for 2 hours. 
3. Season to taste with pepper and additional salt. 
4. Garnish with croutons.