Make the Salisbury Steak Patties. In a large bowl, mix together the ingredients for the Salisbury steak patties.
Brown the Salisbury steak patties. Press the SAUTE button to enable the SAUTE feature and select high. Wait until the display says "Hot" and then add about a tablespoon of oil. Then carefully, lay the ground beef patties flat on the bottom of the inner liner pot of the Instant Pot. (NOTE: You may have to do this in batches.) Cook the ground beef patties on one side for about 3 minutes and then turn and brown the Salisbury steak patties on the other side for another 3 minutes. Then remove the patties to a plate and cover with foil.
Sauté the Mushrooms, Onions and Garlic. Add 2 tablespoons butter and let it melt. Stir in the mushrooms and cook for about 2 minutes. Then add the onions and cook for another 3 minutes or so. Then add the minced garlic and cook for about 1 minute.
Deglaze the Pan. Pour in 1/2 cup of red wine or sherry (or beef broth if not using wine or sherry) and scrape all the bits of food off the bottom of the pan. (NOTE: This is important as it prevents food from burning on the bottom of the pot and helps to prevent receiving the Instant Pot "Burn" message.)
Add the Liquid and Seasonings. Add the rest of the beef broth (if you used some for deglazing) and then add the ketchup, mustard, Worcestershire, Italian Seasoning, and salt and pepper.
Add the Salisbury steak patties back in. Place the Salisbury steak patties back in the pot and cover with liquid as much as possible.
Pressure Cook 7 Minutes High Pressure. Press CANCEL to cancel to sauté function, and then press the MANUAL or PRESSURE COOK button (depending on your model) and select High Pressure, and adjust + or - buttons to set the pressure cook time to 7 minutes. Close the lid and move the pressure release valve to the SEALING position.
Natural Release 10 Minutes. After the Instant Pot has finished pressure cooking, let it release pressure naturally for 10 minutes. (This means that you do NOTHING for 10 minutes.) Then after it has released pressure for 10 minutes, move the pressure release valve to the VENTING position to release the remaining pressure. After it has finished releasing pressure and the pin has dropped, then carefully open the lid and remove the Salisbury Steak patties and place on a plate.
Make The Onion And Mushroom Gravy. Press CANCEL and then press SAUTE and set to High to heat and thicken the gravy. Add the hot sauce, if desired.
Make The Cornstarch Slurry. To thicken the gravy more, make a cornstarch slurry. In a small bowl mix together 2 tablespoons each of cornstarch and water. Stir together until the cornstarch dissolves. Then add the cornstarch mixture into the Instant Pot and stir until it blends in. Let it cook on sauté mode for about 3 to 5 minutes until it thickens. Then press CANCEL, and serve the onion and mushroom gravy over the Salisbury steak Patties.