Preheat your oven to 200°F to keep the cooked steak warm.

Peel the russet potatoes and cut them into thin strips. Rinse under cold water and pat dry.

Heat vegetable oil in a large pot over medium-high heat until it reaches 350°F. Fry the potato strips in batches for 4-5 minutes until golden brown. Drain on paper towels and season with salt.

Crush the black peppercorns coarsely and rub the steak with salt. Press the crushed peppercorns onto both sides of the steak.

Heat olive oil in a large skillet over medium-high heat. Cook the steak for 4-5 minutes on each side for medium-rare. Add butter during the last minute of cooking.

Remove the steak and let it rest for 5-10 minutes, covered loosely with aluminum foil.

In the same skillet, add beef broth and scrape up browned bits. Simmer and reduce by half, then stir in heavy cream and Dijon mustard. Season with salt.

Slice the rested steak against the grain, serve with frites, drizzle sauce over the steak, and garnish with parsley.