Preheat an oven to 350 degrees.
Place the carrots into a baking dish; drizzle with olive oil and sprinkle with salt. Toss to coat. Bake in the oven until just tender, for about 40 minutes.
Meanwhile Heat the butter or ghee over medium-high heat in a medium pot. Add the celeriac and sauté for about 3 minutes. Add in the chicken stock, milk or coconut milk, minced garlic, salt and pepper. Bring to a boil, cover and reduce heat to a simmer. Cook, simmering, for 10 minutes, until the celeriac is tender. Mash with a potato masher or transfer the celeriac and liquid into a food processor and purée until smooth. Season with salt and pepper to taste.
Sprinkle steak with salt. Heat a large cast-iron skillet over high heat. Add oil to pan; and then steak. Cook 3 minutes on each side, or until browned. Reduce heat to medium-low, add butter (or ghee) and crushed garlic to pan. Carefully grasp pan handle using an oven mitt. Tilt pan toward you so butter pools; cook 1 1/2 minutes, basting meat with butter constantly. Remove steaks from pan and let rest 10 minutes. Plate roasted carrots and celeriac mash and slice steak on top.