Preparation Bring potatoes to boil in large pot of water. Reduce heat to medium; cook until tender, about 17 minutes. Drain well. Meanwhile, bring cream, butter, and wasabi paste to simmer in small saucepan over medium heat, stirring until butter melts. Season with salt and pepper. Keep hot. Heat oil in small skillet over medium heat; add green onions and sauté until wilted, about 3 minutes. Set aside. Using potato masher in same large pot or ricer, mash potatoes. Stir in hot cream mixture. Season with salt and pepper. Stir in green onions. DO AHEAD: Can be made 2 hours ahead. Let stand at room temperature. Rewarm in microwave, stirring occasionally. *Available in the Asian foods section of some supermarkets and at Japanese markets nationwide.
Preparation Bring potatoes to boil in large pot of water. Reduce heat to medium; cook until tender, about 17 minutes. Drain well. Meanwhile, bring cream, butter, and wasabi paste to simmer in small saucepan over medium heat, stirring until butter melts. Season with salt and pepper. Keep hot. Heat oil in small skillet over medium heat; add green onions and sauté until wilted, about 3 minutes. Set aside. Using potato masher in same large pot or ricer, mash potatoes. Stir in hot cream mixture. Season with salt and pepper. Stir in green onions. DO AHEAD: Can be made 2 hours ahead. Let stand at room temperature. Rewarm in microwave, stirring occasionally. *Available in the Asian foods section of some supermarkets and at Japanese markets nationwide.