Remove any fat and gristle from the chuck roast and cut into 1 to 2-inch pieces. Set aside.
Combine beef broth, tomato paste, Worcestershire sauce, and mustard in 2-cup measuring cup. Set aside.
Place flour, salt, pepper, and thyme is ziploc bag. Add beef; shake to coat. Heat oil in 12-inch skillet over medium heat. Brown beef in single layer, about 6 minutes. Drain browned beef on paper towels; repeat with remaining beef.
Sauté onions in skillet for 5 minutes. Add garlic; cook for 30 seconds until fragrant. Add 2 tablespoons of remaining seasoned flour; stir to combine. Cook for 1 minute. Add wine; cook, stirring constantly until thickened. Add beef broth mixture; cook stirring constantly until mixture boils.
Transfer beef to pan of slow cooker. Pour on the sauce. Cook on high for 4 hours, or until beef is tender. (See Note 1)
Fifteen minutes before serving, sauté mushrooms in 1 Tablespoon melted unsalted butter over high heat until browned, 3 to 4 minutes. Add to Stroganoff mixture.
Whisk sour cream with 1/4 cup of Stroganoff sauce.(See Note 2) Add to Stroganoff mixture; stir until well combined. Heat briefly. Correct seasonings. Garnish with sliced green onion tops. Serve over buttered noodles. Yield: 4 to 6 servings.