01 - Combine sour cream, horseradish, Dijon mustard, lemon juice, salt, and pepper in a small bowl. Mix thoroughly until smooth and blended. Refrigerate until serving time.
02 - Pat steak cubes dry with paper towels, then season evenly on all sides with 1 teaspoon kosher salt and ½ teaspoon black pepper.
03 - Pour olive oil into a large skillet and heat over high heat until the oil shimmers and just begins to smoke.
04 - Arrange steak cubes in a single layer without crowding. Cook 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 let 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 vigorously to coat evenly in garlic butter. Continue cooking for 1 minute while stirring. Add chopped parsley and toss once more.
07 - Transfer steak bites to a serving platter. Place chilled horseradish cream in a small bowl for dipping. Garnish with additional fresh chopped parsley.