Preheat the oven to 425°F (220°C). Place the baby potatoes in a pot, cover with cold salted water, and bring to a boil. Cook for 15 to 18 minutes, until fork-tender. Drain and let them steam dry for about 5 minutes.
Arrange the potatoes on a parchment-lined baking sheet. Press each one flat with the bottom of a glass or measuring cup until about 1/2 inch thick. Drizzle with the olive oil and sprinkle with the garlic powder, salt, and black pepper.
Roast for 20 to 25 minutes, until deeply golden and crisp at the edges. For extra crispness, broil for 1 to 2 minutes at the end, watching closely. Sprinkle with fresh parsley.
Make the cowboy butter: stir together the softened butter, garlic, Dijon mustard, lemon juice, lemon zest, parsley, chives, smoked paprika, red pepper flakes, black pepper, and a pinch of salt until smooth and well combined. Adjust the seasoning to taste and set aside at room temperature.
Take the steaks out of the fridge 20 to 30 minutes before cooking. Pat them very dry with paper towels and season all over with the kosher salt, black pepper, and garlic powder.
Heat a heavy skillet (cast iron is best) over medium-high to high heat until very hot, then add the olive oil.
Sear the steaks for 3 to 4 minutes without moving them, until a deep crust forms. Flip and cook 2 to 4 minutes more. During the last minute, add the butter and tilt the pan to baste the steaks with the foaming butter.
Check the internal temperature with a meat thermometer: Rare 120-125°F, Medium-rare 125-130°F, Medium 135-140°F, Medium-well 145-150°F. Remember the temperature will rise as the steak rests; medium-rare to medium gives the best texture.
Transfer the steaks to a plate, spoon a little cowboy butter over the top, and rest for 5 to 10 minutes without covering tightly.
Slice the steak against the grain and arrange it on plates with the crispy smashed potatoes. Spoon melted cowboy butter over everything, finish with cracked black pepper and fresh parsley, and serve immediately.