Preheat the oven to 400°F (200°C).
Slice the French baguette into ½-inch thick slices. Arrange the slices on a baking sheet, drizzle with olive oil, and lightly season with salt and pepper.
Bake the baguette slices in the preheated oven for about 8-10 minutes or until golden and crispy.
While the crostini is baking, season the beef tenderloin with salt and pepper. In a frying pan over medium-high heat, sear the beef for about 5-7 minutes on each side or until cooked to your desired doneness (medium rare is recommended).
Remove the beef from the pan and let it rest for about 5 minutes, then slice thinly.
In the same pan, lower the heat, add minced garlic and sauté for about 30 seconds until fragrant.
Pour in the heavy cream, stirring continuously. Gradually add the grated Parmesan cheese, whisking until the sauce is smooth. Fold in the chopped rosemary and let the sauce simmer for another 2-3 minutes until slightly thickened. Season with salt and pepper to taste.
To assemble, place slices of beef tenderloin on each toasted baguette. Drizzle with the Parmesan cream sauce.
Garnish with fresh parsley. Serve immediately.