Cut the steak into approximately 1½-inch pieces.
Pat the steak pieces dry with paper towels.
Season generously with kosher salt and black pepper on all sides.
Heat a large 12-inch stainless steel or cast-iron skillet over medium heat for about 3 minutes.
Add 1 tablespoon of butter and allow it to melt until sizzling and lightly browned.
Arrange the steak pieces in a single layer, leaving space between each piece.
Sear without moving for about 3 minutes until a deep brown crust develops.
Flip the steak bites using tongs or a spatula.
Cook for an additional 2 to 3 minutes or until medium doneness, reaching an internal temperature of 140–145°F (60–63°C).
Transfer the steak bites to a plate.
Reduce the heat to medium-low.
Add the remaining 2 tablespoons butter and chopped garlic to the skillet.
Cook for 2 to 3 minutes, stirring frequently until the garlic becomes fragrant and no longer smells raw.
Scrape up any browned bits from the bottom of the pan for extra flavor.
Remove the skillet from the heat.
Return the Garlic Butter Steak Bites to the skillet and toss until evenly coated in the garlic butter sauce.
Garnish with fresh parsley if desired and serve immediately.