Make Garlic Butter: In the same skillet, reduce heat to medium. Add minced garlic and cook for 1 minute until fragrant. Add butter, thyme, and rosemary. Stir until the butter is melted and the garlic is lightly browned.
Combine: Return the cooked steak bites to the skillet and toss to coat in the garlic butter. Cook for an additional minute to heat through. Season with salt and pepper to taste.
Serve: Plate the steak bites over a bed of mashed potatoes. Spoon any remaining garlic butter from the skillet over the top.