01 - Combine sour cream, horseradish, Dijon mustard, lemon juice, salt, and pepper in a small bowl. Mix thoroughly until smooth and refrigerate until serving.
02 - Evenly coat steak cubes with 1 teaspoon kosher salt and ½ teaspoon black pepper on all sides.
03 - Heat olive oil in a large skillet over high heat until shimmering and slightly smoking.
04 - Arrange steak cubes in a single layer without overcrowding. Sear for 2 minutes per side until deeply browned and cooked through. Work in batches if necessary. Transfer to a plate and cover loosely with foil.
05 - Reduce heat to medium. Add butter to the skillet and melt completely. 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 vigorously to coat evenly with garlic butter. Cook for 1 minute while stirring. Sprinkle with chopped parsley and toss to combine.
07 - Transfer steak bites to a serving platter. Place horseradish cream in a small bowl for dipping. Garnish with additional fresh parsley if desired.