Cook pasta according to package directions. Set aside.
Cut flank steak into ¼" thick x 2" long slices and place in a large bowl. Sprinkle with salt, pepper, cumin and crushed red peppers, stir.
In a large cast iron pan, or frying pan, heat 1 tablespoon of oil over high heat.
Sear beef on both sides then remove from pan.
Melt 2 Tbsp butter over medium heat and saute onions, mushrooms and garlic until onions are translucent and mushrooms are cooked.
Sprinkle flour over onion mixture, stir and cook for a minute or two.
Slowly pour beef broth into pan and stir.
Next, add Worcestershire sauce then add beef back into pan. Stir to combine.
Cook over medium heat, stirring frequently, until sauce has thickened, then remove from heat, add sour cream, stir to combine and serve over cooked pasta.