01 - Whisk together sour cream, horseradish, Dijon mustard, lemon juice, salt, and pepper in a small bowl until smooth. Refrigerate until serving.
02 - Pat steak cubes dry with paper towels, then season evenly with kosher salt and black pepper.
03 - Heat olive oil in a large skillet over high heat until shimmering and just beginning to smoke.
04 - Add seasoned steak cubes in a single layer without crowding (work in batches if necessary). Sear for 2 minutes per side until well-browned and cooked through. Transfer to a plate and cover loosely with foil.
05 - Reduce heat to medium. Add butter to the skillet and melt. Stir in minced garlic and sauté for 30 seconds until fragrant, being careful not to burn.
06 - Return seared steak bites to the skillet. Toss thoroughly to coat in garlic butter and cook for 1 minute. Sprinkle with chopped parsley and toss again.
07 - Transfer steak bites to a serving platter. Serve with chilled horseradish cream alongside for dipping. Garnish with additional fresh parsley if desired.