COOK sweet potatoes in boiling water in 3-quart saucepan 15 minutes or until tender. Drain.
MEANWHILE heat oil in large nonstick skillet on medium-high heat. Add onion; cook and stir 4 minutes. Add curry powder; cook an additional 2 minutes, stirring frequently. Remove from heat.
MASH cooked sweet potatoes. Stir in onion mixture, sour cream and salt.