Set a large pot on the stove and begin boiling the water for the noodles. In a bowl, whisk together beef broth, Worcestershire, Dijon, and flour. This slurry will help thicken the stroganoff sauce.
Slice mushrooms into ¼″ slices.
Slice one medium onion thinly into 2″ pieces.
Next, pat the tri-tip roast dry with paper towels, this helps the tri-tip brown and gives more flavor. Trim excess fat from tri-tip using a small serrated knife.
Slice against the grain into ½” thick, 1” long, pieces. Toss in a bowl with 1 teaspoon salt and ½ teaspoon pepper.
Heat a large dutch oven (or very deep cast iron skillet) on high heat, add 2 tablespoons vegetable oil, be sure to test one piece of meat to see if it sizzles in the pan. Then, carefully saute’ (“fry quickly in a little hot fat”) the tri-tip in batches for 3-5 minutes, using long-handled tongs, move around the pan to brown all sides. PRO TIP: If you overcrowd the pan, it won’t brown, it will steam.
Add one more tablespoon of vegetable oil if the pan is dry before all the tri-tip is brown, and you won’t be cooking the tri-tip all the way it will finish in the last 10 minutes. Oh, and don’t clean the pan, it will be dark brown, this will add flavor! Remove browned tri-tip pieces to a plate. Set aside. Turn heat down to medium heat.
Next, on medium heat, add the chopped onion and stir for 3 minutes. Add one tablespoon butter and add the sliced mushrooms, stir for 3-4 minutes using a wooden spoon. Cook mushrooms till golden brown and scrape the brown caramelized bits off the bottom of the pan. Turn heat down to a low simmer.
At this point, add the noodles to the boiling water (add a little salt to the water) according to package directions for approximately 10-12 minutes. Drain when cooked.
Now add the browned tri-tip and all the drippings into the large pot stir with the mushrooms and onions. Then add the beef stock slurry into the pan. (Optional: add the brandy or white wine). Stir and cook slowly for 10 more minutes. Add additional salt and or pepper to taste. Finally, add sour cream on low heat, and stir just before serving. Serve over hot noodles, garnish with parsley or thyme.