Preheat oven to 450F degrees. Prepare a baking sheet by spraying with non stick cooking spray. Reserve.
Wash and dry kale and potato.
Remove and discard kale stems and roughly chop the leaves. Reserve.
Halved the potato lengthwise and then cut into 1/4-inch thick pieces. Transfer the potato slices to the prepared sheet pan, drizzle with olive oil and season with salt and pepper, tossing to throughly coat. Arrange in a single even layer and roast for 16-18 minutes or until browned and tender when pierced with a fork. Remove from the oven and set aside in a warm place.
White the potato is roasting, heat 2 teaspoons of olive oil in a medium sauce pan, over medium-high heat, until hot. Add the garlic and sauce for about 1 minute or until fragrant. Add the kale and season with salt and pepper. Cook, stirring occasionally, for 1 to 2 minutes, or until slightly wilted. Add 1/4 cup water and continue cooking, stirring occasionally, 2 to 3 minutes, or until wilted and the water has cooked off. Transfer to a bowl and season with salt and pepper to taste, if necessary. Wipe out the pan.
Pat the steaks dry with a paper towel and season generously with salt and pepper on both sides. In the same pan, heat 2 teaspoons of olive oil on medium-high until hot. Add the seasoned steaks and cook 2-3 minutes per side, or until browned and cooked to our desired degree of doneness. Leaving any browned bits in the pan, transfer the steaks to a cutting board and set aside to rest for at least 5 minutes.
While the steaks rest, add the peppercorns, mustard and 1/3 cup of water to the pan. Cook on medium high heat, scrapping the browned bits from the bottom, for 1 to 2 minutes, or until the liquid is slightly reduced in volume. Turn off the heat and stir in the butter until throughly combined. Season with salt and pepper to taste. Set aside in a warm place.
Find the lines of muscle (grain) on the rested steaks and thinly slice crosswise against it. Divide the roasted potato slices, cooked kale and sliced steaks between 2 plates. Top the steaks with the sauce.
Serve immediately!