Preheat a large skillet over medium-high heat and add 1 Tablespoon of olive oil.
Season the beef with salt and pepper and add to the pan when the oil just begins to smoke. It is important to not crowd the pan, so work in batches if needed.
Allow the meat to cook undisturbed for about 1 minute until well browned, then flip. Continue cooking and rotating for around 3 minutes, until the meat is well browned on all sides.
After browned on all sides remove the meat to a plate and set aside. Do not wipe the pan!
Reduce the heat to medium and add two tablespoons of butter to the pan along with any remaining drippings and brown bits from the meat. Add the onion and mushroom. Cook for 6-7 minutes, stirring occasionally.
When all of the liquids from the mushrooms have cooked off and the onions are beginning to caramelize, add the garlic and cook for 30 to 45 seconds until fragrant.
Add the beef stock, Worcestershire sauce, and dried thyme. Scrape up any brown bits from the pan and stir to combine.
In a small bowl mix 1 tablespoon of cornstarch with 2 tablespoons of cold water then whisk into the mushroom mixture. Bring the mixture to a simmer and cook for about 2 minutes, stirring occasionally, until thickened.
Then return the steak tips back to the pan along with any juices from the plate and stir. Cook for 1-2 minutes, then season with salt and pepper to taste before serving.