In this easy recipe, inspired by steak Diane (an American restaurant classic), weʼre searing beef medallions, then using the fond in the pan to make a rich, bright mushroom sauce for spooning on top. Garlic mashed potatoes and sautéed kale make for delicious, simple sides.
1. Prepare the ingredients: Heat a medium pot of salted water to boiling on high. Wash and dry the fresh produce. Large dice the potatoes. Peel the garlic. Using the flat side of your knife, smash 1 clove to flatten. Roughly chop the remaining clove. Peel and thinly slice the shallot. Remove and discard the stems of the kale; roughly chop the leaves. Thinly slice the mushrooms.
2. Cook & mash the potatoes: Add the diced potatoes and smashed garlic to the pot of boiling water and cook 13 to 15 minutes, or until tender when pierced with a fork. Turn off the heat. Drain thoroughly and return to the pot. Add half the butter and a drizzle of olive oil. Using a fork, mash to your desired consistency. Season with salt and pepper to taste. Cover to keep warm.
3. While the potatoes cook, in a large pan, heat 2 teaspoons of olive oil on medium-high until hot. Add the sliced shallot; season with salt and pepper. Cook, stirring occasionally, 1 to 2 minutes, or until softened. Add the chopped kale and 1/4 cup of water; season with salt and pepper. Cook, stirring frequently, 3 to 4 minutes, or until the kale has wilted and the water has cooked off. Transfer to a bowl and season with salt and pepper to taste. Cover with aluminum foil to keep warm. Rinse and wipe out the pan.
4. While the potatoes continue to cook, pat the beef dry with paper towels. Season with salt and pepper on both sides. In the same pan, heat 1 tablespoon of olive oil on medium-high until hot. Add the seasoned beef and cook 2 to 3 minutes per side for medium-rare, or until browned and cooked to your desired degree of doneness. Leaving any browned bits (or fond) in the pan, transfer to a plate and let rest for at least 5 minutes.
5. Make the mushroom sauce: While the beef rests, add a drizzle of olive oil to the pan of reserved fond and heat on medium-high until hot. Add the sliced mushrooms in an even layer. Cook, without stirring, 2 to 3 minutes, or until browned. Add the chopped garlic; season with salt and pepper. Cook, stirring frequently, 1 to 2 minutes, or until softened and fragrant. Add the mustard, verjus, and 2 tablespoons of water (be careful, as the liquid may splatter); season with salt and pepper. Cook, stirring frequently and scraping up any fond, 30 seconds to 1 minute, or until thoroughly combined. Turn off the heat and stir in the remaining butter until melted. (If the sauce seems too thick, gradually add up to 2 tablespoons of water to achieve your desired consistency.) Season with salt and pepper to taste.
6. Serve the rested beef with the mashed potatoes and cooked kale. Top the beef and potatoes with the mushroom sauce. Enjoy!