01 - Combine sour cream, horseradish, Dijon mustard, lemon juice, salt, and pepper in a small bowl. Mix thoroughly and refrigerate until serving.
02 - Season steak cubes evenly with kosher salt and black pepper on all sides.
03 - Heat olive oil in a large skillet over high heat until shimmering.
04 - Add steak cubes in a single layer, working in batches if needed to avoid overcrowding. 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 cook for 30 seconds until fragrant, being careful not to burn.
06 - Return steak bites to the skillet and toss to coat thoroughly in garlic butter. Cook for 1 minute. Add chopped parsley and toss to combine.
07 - Transfer steak bites to a serving platter. Serve with chilled horseradish cream for dipping. Garnish with additional fresh parsley if desired.