Sweet Potato Soup with Coconut Milk & Ginger

Melt the butter in a large saucepot over medium heat and cook the onion for 3 to 4 minutes to soften, but not brown. Add the sweet potato, 3 cups (750 mL) of the stock, the coconut milk, and ginger. Simmer for 25 minutes, until the sweet potatoes are tender. Purée the soup with a handheld blender until smooth, adding the remaining stock if too thick, then stir in the lime juice, and strain thro