Place the halved baby Yukon gold potatoes in a medium saucepan, cover with cold salted water, and bring to a boil. Simmer for 7 to 8 minutes until just fork-tender. Drain completely and let steam-dry for 3 minutes.

Heat 1 tablespoon of olive oil and 1 tablespoon of butter in a large 12-inch cast-iron skillet over medium-high heat. Add the potatoes cut-side down. Cook undisturbed for 4 to 5 minutes until deeply golden brown and crisp on the bottom, then toss to brown the skins for another 2 minutes. Transfer the potatoes to a warm plate and set aside.

Pat the beef tenderloin cubes completely dry with paper towels. Toss the beef with kosher salt, freshly cracked black pepper, smoked paprika, and garlic powder.

Wipe any loose potato bits from the cast-iron skillet and crank the heat to high. Add 2 tablespoons of avocado oil. When the oil begins to lightly smoke, add half of the steak bites in a single layer with space between them.

Sear without moving for 90 seconds to build a deep caramelized Maillard crust. Flip and sear the other sides for an additional 60 to 90 seconds until medium-rare to medium (internal temp 130°F–135°F / 55°C–57°C). Transfer the seared steak to the plate with potatoes, and repeat with the second batch.

Reduce skillet heat to medium-low. Add the remaining 3 tablespoons of European butter along with the minced garlic, fresh rosemary sprigs, and thyme sprigs. As the butter foams and melts, scrape up any caramelized brown steak drippings from the bottom of the pan.

Cook the garlic gently for just 45 to 60 seconds until fragrant, sweet, and golden—do not let the garlic burn. Deglaze with a tablespoon of fresh lemon juice or beef bone broth.

Return the seared steak bites and crispy potatoes to the skillet. Toss everything vigorously for 1 minute so the warm garlic herb butter coats every single morsel.

Remove from heat immediately to prevent overcooking. Garnish generously with freshly chopped Italian flat-leaf parsley and serve sizzling hot straight from the skillet.