1. In a large skillet, cook the bacon over medium heat, stirring occasionally, until crisp, 5 to 7 minutes. Using a slotted spoon, transfer to a paper towel-lined plate.
2. Add the potatoes to the bacon drippings, season with ¼ teaspoon each salt and pepper, and increase heat to medium-high. Cook, tossing occasionally, until browned and tender, 12 to 15 minutes. Transfer to the paper towel-lined plate.
3. Meanwhile, heat the oil in a second large skillet over medium-high heat. Season the steak with ¼ teaspoon each salt and pepper and cook 5 to 7 minutes per side for medium-rare. Let rest at least 5 minutes before slicing.
4. In a small bowl, mix together the blue cheese, sour cream, buttermilk, vinegar, scallion, and ¼ teaspoon each salt and pepper. Divide the lettuce among plates, top with the steak, bacon, and potatoes, and drizzle with the dressing.
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