Combine beef and flour in a large resealable plastic bag and toss to coat evenly.
In a 6 quart saucepan, brown beef in hot vegetable oil. Season with salt and pepper, if desired.
Add diced tomatoes, beef broth, carrots, potatoes, and thyme. Bring to a boil; reduce heat to medium low, cover, and simmer for 1 hour or until beef is tender. Blend in mustard and serve.
French Beef Stew · Dinner Match Lab | Dinner Match Lab