Place the halved baby Yukon gold potatoes into a pot of cold salted water. Bring to a rolling boil over high heat and simmer for 7 to 8 minutes until just fork-tender. Drain thoroughly in a colander and let steam dry for 3 minutes so surface moisture evaporates completely.

Heat 1 tablespoon of olive oil and 1 tablespoon of butter in a large 12-inch cast-iron skillet over medium-high heat. Add the par-boiled potatoes cut-side down. Cook undisturbed for 4 to 5 minutes until deep golden brown and crispy, then toss and cook for another 3 minutes. Transfer potatoes to a warm plate.

Pat the steak cubes completely dry with paper towels. Season evenly with kosher salt, cracked black pepper, smoked paprika, and garlic powder. Wipe out the skillet and heat the remaining 1 tablespoon of olive oil over high heat until lightly smoking. Add the steak bites in a single layer without crowding. Sear undisturbed for 2 minutes to develop a deep caramelized crust, then flip with tongs and sear for another 1 to 2 minutes for medium-rare to medium tenderness.

Immediately return the crispy potatoes to the skillet alongside the steak bites. Reduce heat to medium-low. Drop in the remaining 3 tablespoons of butter, minced garlic, fresh rosemary, and thyme. As the butter foams and sizzles, tilt the skillet slightly and use a large spoon to baste the foaming garlic butter continuously over the steak and potatoes for 1 minute until fragrant. Remove from heat immediately, toss with minced fresh parsley, and finish with flaky sea salt.