Preheat your oven to 375°F (190°C).

In a large pot over medium-high heat, melt butter and olive oil. Season top sirloin with salt and pepper, then sear the beef for 6–8 minutes until browned.

Add chopped onion and carrots to the pot, sauté for 4–5 minutes until onions are translucent.

Sprinkle flour over the mixture, stirring well to coat. Cook for 1–2 minutes.

Pour in apple cider and beef broth, stir to combine and bring to a boil.

Transfer the mixture into an oven-safe pan, cover, and bake for 1 to 1.5 hours until beef is tender.

In the meantime, boil salted water, add potatoes, and cook until fork-tender (15–20 minutes). Drain and let sit for a minute.

In a mixing bowl, add drained potatoes, milk, sour cream, and cheddar cheese. Mash until smooth, then fold in chives.

Once the stew has finished baking, stir and serve over the mashed potatoes.