My sister-in-law prepared this when we were visiting in Santa Barbara, CA. Aren't we all thankful for generous people who share recipes!? My late husband and I loved this dish. At first glance, it looks like it goes on and on, but it's really all three recipes on one page.
In medium bowl, combine steak ingredients, mixing lightly but thoroughly. Shape into 4 oval 1/2" thick patties.
Heat a large non-stick skillet over medium high heat until hot. Place beef patties in skillet; cook 7 - 8 minutes or until no longer pink and juices run clear, turning once. Remove from skillet; keep warm.
Add gravy ingredients to same skillet. Cook over medium heat 3 - 5 minutes or until mushrooms are tender. Serve with Salisbury Steak and Creamy Horseradish Potatoes, below.
Prepare potatoes according to package directions to make 6 servings. Stir in horseradish, salt and pepper immediately after cooking. Serve with Salisbury Steak and Mushroom Gravy.