* 6 small russet potatoes (about 7 ounces each), scrubbed
* 5 tablespoons butter, room temperature
* 12 ounces mushrooms, coarsely chopped
* 2 large green onions, chopped
* 3 ounces cream cheese, room temperature (about 1/2 cup)
* 1/3 cup sour cream
* 1 1/4 cups coarsely grated white cheddar cheese
Preheat oven to 375°F. Pierce each potato in several places with fork. Place all potatoes directly on oven rack and bake until tender, about 1 hour.
Meanwhile, melt 1 tablespoon butter in heavy large skillet over medium heat. Add mushrooms; sauté until beginning to brown, stirring frequently, about 7 minutes. Add green onions; stir until wilted, about 1 minute. Set aside.
Using oven mitts as aid, cut each potato lengthwise in half. Scoop cooked potato flesh into large bowl, leaving skin intact. Add cream cheese, sour cream, and remaining 4 tablespoons butter and mash well. Mix in mushroom mixture and 1/2 cup cheddar cheese. Season to taste with salt and pepper. Mound mashed potatoes in potato skins. Sprinkle each half with 1 tablespoon cheese. Place on baking sheet. (Can be made 1 day ahead. Cover and refrigerate.)
Preheat oven to 375°F. Bake potatoes until heated through and cheese melts, about 25 minutes, or 35 minutes if potatoes have been refrigerated.