1. Bring a large pot of salted water to a boil and cook noodles according to package label directions until tender, about 9 minutes. Drain well.
2. Warm oil in a skillet over medium-high heat. Add beef and cook, stirring, until just cooked, about 4 minutes. Remove beef to a paper towel-lined bowl. Drain all but 2 Tbsp. fat from skillet. Add mushrooms; sauté until tender and water has released, 3 to 4 minutes. Transfer to bowl with beef.
3. In same skillet, melt butter over medium-high heat. Add garlic; sauté 1 minute. Mix flour, 1/4 tsp. salt and 1/2 tsp. pepper. Whisk into butter mixture and cook, whisking constantly, for 1 minute. Mix milk, broth and Worcestershire. Slowly whisk milk mixture into flour mixture. Cook, whisking constantly, until sauce is bubbly and beginning to thicken, 2 to 3 minutes. Reduce heat to low, add sour cream and whisk until heated through.
4. Return beef and mushrooms to skillet. Stir in noodles. Season with salt and pepper, sprinkle with parsley and serve.