Dry-Aged Steaks with Smashed Yukon Potatoes and Buttered Leeks

Boil the potatoes in abundant salted water until they are soft, about 20 minutes (depending on the size). Drain and put them into a large bowl with 2 tablespoons of the butter, the olive oil, sour cream, and 1/4 cup warm milk. Smash with a fork or potato masher until the potatoes are creamy but still have some texture, adding more milk if needed. Season with salt and pepper.

While the potatoes are boiling, cut the white part of the leeks in half lengthwise, then slice into thin half-moons. Rinse well in a colander under running water. Cook the leeks with the remaining 2 tablespoons butter in a skillet over low heat until they are very tender, about 15 minutes. Season with salt and pepper.

Season the steaks with salt and pepper. Grill, broil, or saut to your preferred doneness, 5 to 7 minutes per side for medium-rare. Transfer the steaks to a plate and let stand for 5 minutes while you prepare the plates.

On each of four plates, mound the leeks in the center, using the back of a large spoon to form them into a ring. Mound the potatoes in the center. Cut the steaks crosswise into slices and arrange them over the top of the potatoes and leeks. Drape the mushrooms over the steak, if using.