Bring a large pot of salted water to boil. Cook egg noodles according to package instructions. Drain, rinse, and set aside.
Season steak cubes with salt and pepper. Toss with 1 tablespoon of the flour.
Heat the olive oil in a saucepan over medium high heat. Sear the steak in small batches, about 1 minute per side. Remove the steak from the pan and set aside.
Reduce heat to medium and add butter and onion. Cook for 4 minutes, or until tender and translucent.
Add mushrooms and garlic and cook for an additional 4 minutes. Add remaining flour and cook for 1 minute.
Add stock, Worcestershire sauce, dijon mustard, and thyme. Bring to boil and then reduce heat and simmer for 5 minutes, or until thickened.
Add beef back to the pan and cook for 1 minute. Gently stir in sour cream
Fold in noodles or serve on a bed of noodles. Garnish with fresh thyme sprigs.