Preparation Preheat oven to 375°F. Place potatoes on oven rack. Bake until tender when pierced with fork, about 50 minutes. Scoop out pulp from potatoes into heavy large saucepan; discard skins. Add 3 tablespoons butter to potatoes and mash well. Mix in mustard. Gradually add milk and mash until smooth. Stir potatoes over medium-low heat until heated through, about 5 minutes. Mix in green onions. Season to taste with salt and pepper. Transfer to bowl. Top with remaining 1 tablespoon butter and serve.
Preparation Preheat oven to 375°F. Place potatoes on oven rack. Bake until tender when pierced with fork, about 50 minutes. Scoop out pulp from potatoes into heavy large saucepan; discard skins. Add 3 tablespoons butter to potatoes and mash well. Mix in mustard. Gradually add milk and mash until smooth. Stir potatoes over medium-low heat until heated through, about 5 minutes. Mix in green onions. Season to taste with salt and pepper. Transfer to bowl. Top with remaining 1 tablespoon butter and serve.