01 - Whisk together sour cream, horseradish, Dijon mustard, lemon juice, salt, and pepper in a small bowl. Cover and refrigerate until serving.
02 - Pat steak cubes dry with paper towels and season evenly with kosher salt and black pepper.
03 - Heat olive oil in a large skillet over high heat until shimmering. Add steak cubes in a single layer, searing for 1-2 minutes per side until browned and just cooked through. Remove to a plate and tent with foil.
04 - Reduce heat to medium. Add butter to the skillet and once melted, add minced garlic. Sauté for 30 seconds until fragrant.
05 - Return steak bites to the skillet and toss to coat in the garlic butter for about 1 minute. Sprinkle with chopped parsley and serve immediately with the chilled horseradish sauce on the side.