Prepare the Mashed Potatoes:

1. Boil the Potatoes: In a large pot, cover the potato chunks with cold water and add a generous pinch of salt. Bring to a boil over high heat, then reduce to medium heat and cook for 15-20 minutes, or until the potatoes are fork-tender.
2. Drain and Mash: Drain the potatoes and return them to the pot. Mash them with a potato masher or ricer until smooth.
3. Add Cream and Butter: Stir in the heavy cream, butter, and sour cream (if using) until well combined. Season with salt and pepper to taste. Cover and keep warm.

Cook the Steak Bites:

4. Heat the Pan: Heat a large skillet over medium-high heat. Add olive oil and 1 tablespoon of butter, allowing the butter to melt and sizzle.
5. Sear the Steak: Season the steak bites generously with salt and pepper. Add them to the skillet in a single layer, being careful not to overcrowd the pan. Sear for 1-2 minutes on each side until a golden crust forms. Remove the steak from the skillet and set aside.
6. Make the Garlic Butter Sauce: Lower the heat to medium. Add the remaining 3 tablespoons of butter to the skillet. Once melted, stir in the minced garlic and thyme, cooking until fragrant (about 1 minute).
7. Coat the Steak: Return the steak bites to the skillet, tossing them in the garlic butter sauce for 1-2 minutes to reheat and coat.

Serve:

8. Plate the Dish: Spoon a generous portion of mashed potatoes onto each plate and top with the garlic butter steak bites. Drizzle any remaining sauce from the skillet over the top.
9. Garnish and Serve: Sprinkle with fresh parsley or chives and serve hot.