1. In a large pot of salted water, cook noodles according to pkg. directions (do not overcook); near the end of cooking time, scoop approx. 1 cup pasta cooking water from the pot and reserve.
2. While pasta cooks, heat oil in an extra-large sauté pan over medium-high heat, swirling to coat. Add mushrooms to the sauté pan; cook until browned (4-5 min.).
3. Season mushrooms with salt and pepper; transfer to a medium bowl and set aside.
4. Add beef to the sauté pan; cook and stir until meat is hot and falling apart (2-3 min.).
5. Transfer beef to the bowl with mushrooms; set aside. Add demi-glace and reserved hot pasta water to the pan, scraping up browned bits from the bottom.
6. Reduce heat to medium; simmer until sauce is reduced by ½ (about 4 min.).
7. Whisk in butter.
8. Using a slotted spoon, transfer cooked pasta from the pot to the sauté pan with the sauce; stir and simmer until thickened (about 2 min.).
9. Adjust seasoning to taste. Stir mushrooms and beef into the pasta.
10. Stir in sour cream until incorporated.
11. Garnish with thyme; serve immediately.

Tasty Tip:

• Kowalski's Signature Beef Demi-Glace is often sold and may be stored at home in the freezer. Thaw in the refrigerator or microwave before use or simply drop the frozen product into the pan and cook a few minutes longer to melt it.