To make the celery root puree: Melt the butter in a heavy large saucepan over medium heat. Add the celery root, milk, cream, shallots, and salt. Simmer very gently, uncovered, until the celery root is tender enough to mash with a spoon, stirring occasionally, about 30 minutes.
Using a slotted spoon, transfer the celery root to a blender or food processor. Blend until smooth, adding enough of the cooking liquid to thin the puree to the desired consistency.
To prepare the steaks and spinach: Preheat the oven to 400°F. Coarsely crush the peppercorns with a mortar and pestle. Transfer the crushed peppercorns to a sieve and sift the pepper into a bowl to remove any finely ground pieces of pepper; reserve the fine pepper for another . Sprinkle the coarse pepper grinds over a plate. Sprinkle the steaks with salt then set the steaks atop the pepper and press, coating both sides and flattening the steaks slightly.
Heat a large ovenproof sauté pan over medium-high heat. Add the oil then add the steaks. Cook until the steaks are caramelized and golden brown on both sides and around the perimeter, about 5 minutes. Transfer the pan to the oven and continue cooking the steaks to desired doneness, about 4 minutes for medium-rare doneness. Transfer the steaks to a plate to rest for 5 minutes.
Add the spinach to the same sauté pan and cook just until the spinach wilts, about 1 minute. Divide the spinach among 4 plates.
To make the sauce: Heat the oil in the same sauté pan over medium-high heat. Add the shallots and sauté until tender, about 2 minutes. Add the red wine and thyme and simmer until reduced by half. Return the steaks to the pan and baste the steaks with the sauce. Set the steaks atop the spinach on each plate. Stir the butter into the sauce to blend.
Spoon the celery root puree alongside the steaks and spinach. Spoon the sauce over the steaks and serve.
Read more: http://www.kitchendaily.com/recipe/father-s-day-pepper-crusted-filet-mignon-142941#ixzz0uk7wWmyN
