Turn the Ninja Foodi or Instant Pot on high sear/sauté and allow the pot to heat up for about 5 minutes.
In a large mixing bowl combine the ground beef, seasonings, Worcestershire sauce, chopped onions, egg, sour cream, and panko. Mix well.
Form 6 hamburger patties that are about ¼-½" thick. If you want larger servings, only make 4 patties.
Add olive oil to the hot pot and let heat for 2-3 minutes. If you are using a stainless steel inner pot, reduce heat to medium or medium high.
Place 3 patties in the inner pot and allow to brown for about 2 minutes, flip and brown the other side. Move those patties to the side of the pot and add the remaining patties in batches. As the patties brown and start to cook they shrink. As they are done browning on both sides, move them to the side and stack them so you have room for the onions.
Gravy
Add the sliced onions to the pot and sauté them for 1-2 minutes. Add in the crushed garlic cloves. Add in the mushrooms if you are using them.
Deglaze the pot with 1 cup beef broth and scrape the bottom to release any browned bits (fond) at the bottom.
Add in the worcestershire sauce. This can be added before or after pressure cooking.
Put the pressure lid and make sure the valve is to the sealed position. Pressure Cook on high for 5 minutes. When the time is up, immediately release the pressure.
Mix the remaining ½ cup beef broth with the cornstarch to make a slurry. Add to the inner pot and stir. The heat of the liquid after pressure cooking should be enough to activate the cornstarch and thicken the gravy. If it is not thickening, turn on sear/sauté on high and bring to a boil and then turn the heat off.
If you want your sauce thicker, you can add more cornstarch mixed with either water or beef broth. Once the sauce is the thickness you like, stir in the sour cream.
Stove Top DirectionsFollow the same instructions to form the patties. Heat oil in large skillet and brown the patties on both sides. Add in the onions, mushrooms (if using), and garlic and sauté for a few minutes. Deglaze the pot with 1¾ cups of beef broth. Add in the Worcestershire sauce. Cover and simmer for about 15 minutes.Combine the remaining ¼ cup of beef broth with cornstarch and make a slurry. Pour the slurry into the pan and stir. Bring to a boil and stir to thicken the sauce. Turn the heat off and stir in the sour cream. Slow Cook DirectionsFollow the same instructions to form the patties. Brown the patties on both sides either in a skillet or in the slow cooker if it has that function. Add in the onions and mushrooms (if using) along with the smashed garlic. Deglaze with 2 cups of beef broth. Mix together ¼ cup of beef broth with 2 Tablespoons of cornstarch and pour the slurry into the slow cooker. Stir to combine.Slow Cook on low heat for 4-6 hours or until the ground beef has cooked through and the gravy has thickened.