Preheat the oven to 400°F (200°C). Cut the top off the head of garlic to expose the cloves. Drizzle with olive oil and wrap in aluminum foil. Roast in the oven for 30-35 minutes until soft. Allow to cool, then squeeze the garlic cloves into a bowl.

In the bowl with the roasted garlic, add mayonnaise, lemon juice, salt, and pepper. Mix until smooth and well combined. Set aside.

Cut the russet potatoes into matchstick shapes. Soak them in cold water for 30 minutes to remove excess starch. Drain and pat dry. In a large bowl, toss the potatoes with 1 tablespoon of olive oil, chopped rosemary, and salt.

Preheat the oven to 425°F (220°C) and line a baking sheet with parchment paper. Spread the fries in a single layer on the sheet. Bake for 25-30 minutes, flipping halfway through, until golden brown and crispy.

Crush the black peppercorns using a mortar and pestle or a heavy skillet until coarsely ground. Season the filet mignon steaks with salt and press the crushed peppercorns onto both sides of the steaks.

Heat a skillet over medium-high heat and add 2 tablespoons of olive oil. Once hot, add the steaks. Cook for 4-5 minutes on each side for medium-rare, or until desired doneness is reached. Use a meat thermometer for accuracy (130°F for medium-rare). Let the steaks rest for 5 minutes before serving.

Plate the filet mignon alongside the rosemary-salted matchstick fries. Serve with a generous dollop of roasted garlic aioli on the side.