2 (8-ounce) beef filets, preferably 1 1/2-inches thick, at room temperature

1/4 cup chicken stock or white wine

4 tablespoons unsalted butter, divided

1 pound mixed mushrooms, cleaned and sliced

1 large onion, sliced into half moons

4 thick slices good-quality bread (I used a French loaf)

1 cup spicy greens, such as arugula or watercress

Kosher salt and freshly ground pepper, to taste

Preheat oven to 325 F. Line a baking sheet with foil and set aside.

Heat two tablespoons of oil in a heavy skillet over medium-high to high heat. Pat the filets very dry and season the side facing up generously with salt and pepper. When the oil is shimmering, place the filets, seasoned side down, in the skillet. Season the top with additional salt and pepper.

Cook the steaks without disturbing until a deep golden brown crust has formed, 3 to 5 minutes. Flip the steaks and allow to cook for another minute or so. Place the steaks on the baking sheet (they should still be on the rare side, about 120 F on an instant read thermometer) and transfer to the oven.

Return the skillet to high heat. Add the stock or wine and swirl to remove any caramelized bits from the bottom of the pan. Lower heat to medium and add 2 tablespoons butter. Add the mushrooms and onions and sprinkle with salt and pepper. Cook the mushroom mixture, stirring frequently, until tender, 10 to 12 minutes. Transfer to a plate.

Remove steaks from the oven and check their temperature: if they have reached 130 F, remove them from the baking sheet and set aside to rest; if not, return them, along with the mushroom mixture, to the oven.

Melt the remaining two tablespoons butter in the skillet. Add the bread and cook until toasted and golden brown on each side. Remove the steaks and mushroom mixture from the oven. Place about 1/4 cup greens over each piece of bread, followed by 1/4 of the mushroom mixture. Thinly slice the steaks lengthwise and arrange over the bread; pour any juices from the cutting board over the top.

Recipe Notes

Although I usually prefer a fattier cut, such as a rib eye, a filet really is the best choice for this recipe -- its mild, buttery taste will not be overwhelmed by the other flavors.

(Nealey Dozier is a writer for TheKitchn.com, a nationally known blog for people who love food and home cooking. Submit any comments or questions to kitchn@apartmenttherapy.com.)