Potatoes
Preheat oven to 425°F (220°C).
Toss potatoes with olive oil, paprika, salt, and pepper.
Spread in a single layer on a baking sheet.
Roast 30–35 minutes, flipping once, until golden and crisp.
Steak
While potatoes roast, season steak generously with salt and black pepper. Let rest at room temperature 20–30 minutes.
Heat a heavy skillet over medium-high heat and add neutral oil.
Sear steak 3–5 minutes per side for medium-rare, depending on thickness.
Optional: Add butter during the last minute and baste.
Remove steak and rest 5–7 minutes, tented loosely with foil.
Chimichurri Salsa
In a bowl, combine parsley, cilantro, garlic, red pepper flakes, salt, and pepper.
Slowly drizzle in olive oil until loose and spoonable.
Taste and adjust seasoning; add lemon zest if desired.
To Serve
Slice steak against the grain.
Serve with roasted potatoes and spoon chimichurri generously over the steak.