Sweet Potato Vichysoisse with Chipotle Crema

Ingredients

• 4 cups sliced leeks, the white part
• 4 cups sweet potatoes or yams (1 1/2 pounds), peeled and roughly chopped
• 6 to 7 cups water
• Kosher salt and freshly ground black pepper
• Ice cubes
• 1 cup crème fraiche, divided
• 2 tablespoons milk, if needed
• 1 tablespoon minced chives
• 2 teaspoons chipotle en adobo
• 1 ½ tablespoons tomato paste