Place sweet potatoes in a large pot and cover with cold water. Bring to a boil then reduce heat to low. Simmer until potatoes are fork tender, 7-9 minutes. Strain potatoes and set aside to cool slightly.
Add all remaining ingredients to a food processor (yogurt through pepper) as well as the strained sweet potatoes. Pulse on high until smooth and creamy.
Check for seasoning and adjust accordingly before serving.
If you don't have a food processor, you can puree with an immersion blender or a high speed blender. They also taste delicious with a hand-held potato masher.