In a large skillet, heat the olive oil over medium-high heat. Add the sliced onions and cook for about 3 minutes until translucent.
Add the minced garlic and sliced mushrooms to the skillet, cooking until the mushrooms are tender, about 5 minutes.
Add the beef strips to the pan, seasoning with salt and pepper. Cook until browned, around 5-7 minutes, stirring occasionally.
Stir in the Worcestershire sauce, Dijon mustard, beef broth, and paprika. Bring the mixture to a simmer, then reduce heat and let it cook for about 10 minutes, allowing the sauce to thicken.
Remove from heat and slowly stir in the sour cream until fully combined. Taste and adjust seasoning if needed.
Preheat the oven to 400°F (200°C). Place the sliced French bread on a baking sheet and spread softened butter on both sides.
Bake the French bread in the preheated oven for about 8-10 minutes, or until golden and crisp.
To serve, spoon the beef stroganoff mixture over the crunchy French bread slices. Garnish with freshly chopped parsley.