Season the steak with salt and pepper, generously. Heat a large skillet over medium-high heat. Drizzle in a splash of the oil. Once hot, place the steak in the oil and sear for about 4-6 minutes. Shake the pan, if the steak shifts in the pan it is ready to flip. Repeat on the other side. When the steak is seared on both sides, remove, place on a cutting board and cover with a large lid or foil. It will rest and the juices will continue to cook through. Let it be very rare at this point, just seared on both sides.

While the steak is cooking and resting, slice the onion and mushrooms into long strips.

As soon as the steak is removed from the pan, add in a splash more oil and reduce the heat to medium. Add the onions and sauté lightly until they begin to have color. Remove the leaves from the thyme sprigs and add half to the onions. Add a splash of the beef broth and continue to sauté for 5 more minutes until they are slightly tender. Remove the onions, add a splash more oil to the pan and sauté the mushrooms, trying to get color on each side.

When the mushrooms are done add the onions back in. Deglaze the pan, by adding in the white wine. While it begins to simmer, slice the steak in thin pieces, against the grain. If you are unsure how to do this, cut a slice and see if there seems to be almost ridges?this is the grain. Imagine the steak is a deck of cards and you want a slice of each card. Continue slicing in that direction.

Combine the remaining beef broth, Worcestershire sauce, and cornstarch stirring until the cornstarch dissolves. Pour this into the pan with the mushrooms and onions, toss everything for a while to allow the cornstarch to cook and thicken. Add a sprinkle of salt and pepper to taste as well.
If you can taste the powder-y cornstarch continue cooking. If it begins to look dry add a splash more of the beef broth or white wine.

Add the sour cream at this point, allow it to melt and coat the mess of vegetables. Next add in the steak strips and toss to coat with the mixture. Continue cooking until the steak is cooked through.

Serve on top of Whole Wheat Pasta, Brown Rice Pasta, or Wild Rice.