Heat the olive oil in a skillet over medium heat. Add the diced onion and cook until it becomes translucent, about 3 minutes.

Stir in the minced garlic and sliced mushrooms. Cook for another 5 minutes until the mushrooms are tender.

Add the sliced beef to the skillet and cook until browned, about 3-5 minutes. Season with salt and pepper to taste.

Sprinkle the flour over the beef mixture and stir well to combine. Cook for an additional 2 minutes to eliminate the raw flour taste.

Gradually pour in the beef broth while stirring, then add the Worcestershire sauce and Dijon mustard. Bring the mixture to a simmer and cook until it thickens, approximately 5 minutes.

Remove the skillet from the heat and stir in the sour cream until fully incorporated. Adjust seasoning if needed.

While the stroganoff is finishing, preheat your oven to 350°F (175°C). Slice the French bread into 1-inch thick slices. Spread softened butter on each slice.

Place the buttered bread slices on a baking sheet and toast in the oven for about 5-7 minutes, or until golden.

To serve, place a slice of toasted French bread on each plate and spoon the beef stroganoff mixture on top. Garnish with chopped parsley.