Next, prep and measure out the rest of the ingredients. It’s important to have everything ready, as the steps go quickly until you add in the beef stock. Cut the flank steak into 1-1½in (2.5-3.8cm) thick slices and place them back in the fridge. Then, prepare your veggies.
For the onion, chop off the top and bottom to create a flat surface. Set the onion down on one of the flat sides and slice it in half. From there, lay each half of the onion down with the centers on your cutting surface. Then, make vertical slices in whatever thickness you’d like to have in your final dish.
To clean the mushrooms, de-stem them by pushing and then pulling the stem to pop them free of the cap. Once all are de-stemmed, run each mushroom under the faucet, rubbing your thumb over the cap to remove any dirt. Lastly, slice the mushrooms into ¼-½in (.6-1.2cm) slices. They can be piled into one big bowl and set aside.
Now, measure out the salt separately and, then, mix the marmite, grated garlic, black pepper, Tamari or soy sauce, and anchovy together into a small bowl, until it forms what I like to call “umami paste,” and set that aside as well. Lastly, make sure the beef stock is warmed into liquid form.
Retrieve the meat pieces from the fridge. Pat the pieces of meat dry with some paper towel and set them aside. Next, place an enameled Dutch oven or oven safe pot on your stove top and turn the heat to medium high. Once the pot is hot, add in the first round of neutral oil and let it heat up as well. Then, start adding chunks a few at a time. Don’t over crowd the pot or you won’t get a good sear. Sear each side of the beef, building up a nice crust around their outsides. If any browned bits develop on the bottom of the pot and look or smell like they are getting close to burning, pour some water, a bit at a time, into the pot where it’s getting dark. Scrape the fond (browned bits) up or move the meat around to collect it. Work in batches until all of the meat is seared and set it aside.
Once all of the meat is cooked, add in the rest of the oil and then the mushrooms. They will release liquid as they cook and eventually start too brown, deepening their flavor. This should take around 30 minutes. When the pot is mostly dry, add the umami paste to the mushrooms, and scrape it around the pot with your flat-bottomed spatula for 1-2 minutes. The paste should cook and darken a bit before it also begins to stick to the pot.
At this point, turn the heat to medium, toss in the diced onion and sprinkle the kosher salt over them while stirring and scraping. The onions will soften and release their liquid, to help deglaze the pan again. When the onions turn a bit translucent, 15-20 minutes, add in the mushroom gravy paste and the beef stock. Mix the stew until the liquid is visually smooth and uniform. Cover the pot with the lid and turn the stovetop down to low. The stew will thicken more once it starts to simmer.
Next, either cut the meat into thin ¼in (.6cm) slices or chop it into small, bite-sized ½in (1.3cm) cubes, depending on what you prefer. From there, add the meat to the stroganoff, stir everything together, and add the lid back on. Let the beef stroganoff simmer in the Dutch oven for 2 hours. Make sure it does not come to a rolling boil or the meat will toughen up.
The stroganoff is ready to finish with sour cream when the beef is tender to the teeth or easy to cut with a fork, but isn’t actively falling apart without help. Measure out the sour cream and add it to a large cup or small bowl. Very slowly, ladle some stew broth into the sour cream. Stir immediately and continuously, tempering the sour cream. Once the sour cream has enough broth that it is watery and very warm (most times I’ve more than doubled the volume of ingredients in the bowl) whisk it back into the Dutch oven, stirring constantly.
At this point, just let the stew stay warm on low with the lid off while you cook a starch to eat with it.