Combine first ten ingredients and mix well. Shape into 2 oval loaves and place on broiler pan or in rack in shallow roasting pan. Bake in 350° oven 45 to 50 minutes. Meanwhile, make the Stroganoff Sauce. In fry pan, sauté onion in butter until tender. Add mushroom slices and sauté 2 to 3 minutes. Stir in flour, mustard and salt. Add water and seasoning base and cook, stirring constantly, until thickened and bubbly. Stir in sour cream. Heat but do not boil. Place twin meat loaves on bed of cooked noodles and serve with sauce.