Prepare the Shoestring Fries: Peel the russet potatoes and cut them into thin, matchstick-sized pieces. Rinse the potato strips in cold water to remove excess starch and pat them dry with paper towels.

In a large pot, heat vegetable oil to 350°F (175°C). Fry the potato strips in batches until golden brown and crispy, about 3-4 minutes per batch. Remove the fries from the oil and drain on paper towels. Season with sea salt and a sprinkle of truffle salt. Set aside.

Cook the Filet Mignon: Allow the filet mignon steaks to come to room temperature, about 30 minutes before cooking. Pat them dry with paper towels and season generously with salt and black pepper.

In a large skillet, heat olive oil over medium-high heat. Once hot, add the steaks to the skillet and sear them for 4-5 minutes on each side for medium-rare, adjusting time for desired doneness.

During the last minute of cooking, add the butter and rosemary sprigs to the skillet. Spoon the melted butter over the steaks as they finish cooking for extra flavor.

Make the Savory Mushroom Jus Sauce: In a small saucepan over medium heat, melt the butter. Add the minced garlic and sauté for about 30 seconds until fragrant. Add the chopped mushrooms and cook until softened, about 5-7 minutes.

Pour in the beef stock, soy sauce, and balsamic vinegar. Bring to a simmer and reduce the sauce by half, about 10-15 minutes. Season with salt and black pepper to taste.

Plating: On each plate, place a filet mignon steak, drizzle with the savory mushroom jus sauce, and serve alongside a generous portion of truffle-salted shoestring fries.