Begin by boiling the potatoes. In a large pot, add the potato chunks and cover them with water. Bring to a boil over medium-high heat. Cook for about 15-20 minutes, or until fork-tender.
While the potatoes are boiling, heat a large skillet over medium-high heat. Add the olive oil to the skillet.
Season the steak cubes with salt and black pepper. Once the oil is hot, add the steak bites to the skillet, making sure not to overcrowd the pan. Sear the steak for about 2-3 minutes on each side, or until browned and cooked to your preferred level of doneness. Work in batches if necessary.
Reduce the heat to low and add the butter and minced garlic to the skillet with the steak. Stir to combine and let the garlic cook for about 1-2 minutes until fragrant.
Once the potatoes are finished cooking, drain them in a colander. Return the drained potatoes to the pot. Add in the milk, unsalted butter, salt, and pepper. Mash until smooth and creamy.
Serve the garlic butter steak bites hot, garnished with chopped fresh parsley if desired, alongside a generous scoop of creamy mashed potatoes.