Season beef with salt, pepper and thyme.
In a frying pan, on medium-high heat, add oil and sear beef in batches, set aside.
In the same pan on medium heat, add butter. Sautė onion for 3-4 minutes and add garlic; cook for 2-3 minutes.
Add carrots, celery and mushrooms; cook for approximately 5 minutes.
Stir in tomato paste then add flour and mix thoroughly. Slowly add broth while mixing and scraping anything stuck to the pan.
Add the seared beef back to the pan and bring up to a simmer and cover for approximately 1-2 hours.
Remove the lid and increase heat to medium to reduce liquid to desirable thickness about ½ hour; stirring occasionally.
Adjust seasoning if needed and serve over mashed potatoes or noodles.
