Sweet Potato Soup

I saw this soup on CityLine, and I have never drooled over a cooking segment more. I was pumped to find the recipe on their website and was looking for a reason to make it! Michael & Nancy came to dinner tonight to celebrate that they are expecting their first baby in the spring, and I knew this soup would be right up their alley.

2 T butter
1 1/3 C diced onion
6 C peeled and diced sweet potato (3 potatoes)
2 T grated fresh ginger
1 can coconut milk
3 C chicken stock
2 T lime juice
2 t cayenne pepper sauce (Frank's red hot, or similar)
1/4 cup plain yogurt

Melt butter in a large saucepot over medium heat and cook onion 3-4 minutes to soften, but not brown. Add sweet potato, ginger, coconut milk and stock. Simmer 45 minutes, until sweet potatoes are tender. Purée until smooth with a hand blender. Return to heat and stir in lime juice & cayenne sauce. Ladle into bowls and top with a swirl of yogurt.