Make restaurant-quality filet with this peppery, mustard marinade. Served alongside a mushroom ragù and drizzled in claret sauce, you'll hardly believe you made this dish at home.
Heat the olive oil in a saucepan and add the garlic, onion, carrot, celery, bay leaves, peppercorns, and salt. Sauté over medium heat for 6 to 7 minutes, or until the vegetables are tender. Add the wine, bring to a boil, and simmer over medium-low heat until reduced by 2/3, about 40 minutes. Add the stock and reduce by 2/3, about 40 minutes longer. Strain into a clean saucepan and continue to reduce until about 1 cup remains and the sauce is thick enough to coat the back of a spoon. Keep warm.
Heat 2 tablespoons of the olive oil in a sauté pan and add the shiitake mushrooms. Sauté over medium-high heat for 3 minutes, stirring frequently. Stir in the corn and sauté for 2 minutes longer. Remove from the heat. Heat the remaining tablespoon of the olive oil in a saucepan and sauté the garlic over medium heat for 3 minutes. Add the quinoa and stir with a wooden spoon to coat thoroughly. Add the stock and 2 cups of water, and bring to a simmer. Cook for about 10 minutes, or until the liquid is absorbed and the quinoa is almost dry but still moist. Add the mushroom-corn mixture and season with salt and pepper.
Place the olive oil, mustard, peppercorns, and salt in a bowl and spread the mixture onto both sides of the steaks. Let sit at room temperature while preparing the ragù.
Preheat the broiler. When hot, broil the steaks for about 5 minutes for medium-rare, about 6 minutes for medium, or to the desired doneness. Turn the steaks once to ensure even cooking. Transfer to serving plates, spoon the sauce around, and garnish with the marjoram. Serve with the ragù.