Preheat your grill or a cast-iron skillet over medium-high heat.

In a bowl, mix the chopped sage with olive oil. Rub this mixture all over the flat iron steaks, ensuring they are evenly coated. Season generously with salt and black pepper.

Grill or sear the steaks for about 4-5 minutes per side for medium-rare, or adjust cooking time to your desired doneness. Once cooked, remove from heat and let rest for 5 minutes before slicing.

Preheat your oven to 425°F (220°C).

Wash and peel the russet potatoes. Cut them into thin matchstick shapes.

In a bowl, toss the matchstick potatoes with olive oil, lemon zest, and salt until evenly coated.

Spread the fries in a single layer on a baking sheet. Bake for 20-25 minutes, flipping halfway through, until golden and crispy.

Remove from the oven and immediately sprinkle with grated Parmesan cheese.

In a saucepan over medium heat, combine the beef broth and whole black peppercorns. Bring to a simmer and let it reduce slightly for about 5-7 minutes.

Whisk in the Dijon mustard and butter, then season with salt to taste. Remove from heat and strain if desired, to remove the peppercorns.

Slice the rested flat iron steak against the grain and serve alongside the lemon-Parmesan matchstick fries.

Drizzle the savory peppercorn jus over the steak and enjoy!