Boil potatoes in salted water until fork-tender (about 12–15 minutes). Drain well.

While the water is boiling for the potatoes, mix all the chimichurri sauce ingredients together in a bowl and let it sit so the flavors come together. Taste and adjust salt or vinegar

Once potatoes are soft, drain and return to the pot. Mash while hot, then mix in butter first so it melts in. Add warm milk gradually until smooth and creamy. Stir in sour cream for extra richness. Season with salt and pepper to taste.

Pat the steak dry so it sears well. Toss with salt, pepper, paprika, and garlic powder.

Heat a cast iron or heavy pan over medium-high heat until very hot. Add olive oil, then steak in a single layer (don’t overcrowd—do batches if needed).

Sear 2–3 minutes without moving, then flip and cook another 1–2 minutes for medium-rare to medium.

Lower heat, add butter and garlic, and toss the steak bites until glossy and coated. Finish with a pinch of chili flakes if you want heat.

Assemble by layering mashed potatoes first, steak bites on top, and then a drizzle of chimichurri sauce. Enjoy!