Place potatoes in a Dutch oven, and cover with water; bring to a boil. Reduce heat, and simmer 30 minutes or until tender; drain.
. Preheat oven to 400°.
. Heat oil in a large nonstick skillet coated with cooking spray over medium-high heat. Add onion and garlic; sauté 3 minutes. Add sliced mushrooms, 1/2 teaspoon salt, and 1/2 teaspoon pepper; sauté 5 minutes or until tender. Add broth; cook 5 minutes, stirring occasionally.
. While mushroom mixture cooks, combine ricotta, 1 cup mozzarella, and egg white in a bowl; stir well. Combine Alfredo sauce, basil, and oregano in another bowl; stir well.
. Peel potatoes, and cut into 1/4- inch slices. Arrange half of potato slices in a 13 x 9-inch baking dish coated with cooking spray; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon pepper. Top with half of mushroom mixture. Spread half of ricotta mixture evenly over mushroom layer. Spread half of Alfredo sauce mixture over ricotta layer. Repeat procedure once, ending with Alfredo sauce mixture. Cover with foil coated with cooking spray. Bake at 400° for 30 minutes. Uncover and sprinkle with remaining 1 cup cheese. Bake 15 minutes or until cheese melts and casserole is bubbly. Let stand 10 minutes before serving.