1 large bone-in ribeye steak (1 ¾-2 pounds), about 1 ½” thick
2 teaspoons vegetable oil
3 tablespoons unsalted butter, softened
1 tablespoon olive oil
4 large whole garlic cloves, peeled
1 sprig rosemary (optional)
+ Kosher salt and freshly ground black pepper to taste
Season all sides of the steak VERY generously with salt and pepper; let sit to come to room temp for an hour if you have time (even half an hour helps).
Heat a large (10- or 12-inch) heavy cast iron skillet over high heat until VERY hot but not smoking. Add the vegetable oil to the skillet, and carefully tilt the skillet to evenly coat the surface in oil. Add the steak to the skillet and cook, not moving, until a crust forms underneath, 3–4 minutes.
Flip the steak, then add the butter, olive oil, and garlic cloves to one side of the skillet; the butter should melt pretty much immediately and you can now butter-baste the steak, using an oven mitt to tilt the pan and a large spoon (a large metal soup spoon with a long handle is great) to scoop up some of the butter-oil mixture and spoon it over the steak a few times before flipping. Continue to do this, basting and flipping, until the steak is medium-rare (when it registers 130°F on an instant-read thermometer) and a deep, golden crust has formed on both sides and the garlic is a deep brown, 7–9 minutes. (Remove the garlic before the steak if it is golden brown, not letting it burn.) Add the rosemary in the last 1–2 minutes of cooking, if using.
Remove the pan from the heat, transfer the steak to a rimmed baking sheet or cutting board (ideally with a channel for juice) to rest for 5 minutes. Slice the steak against the grain, transfer to a serving platter, add the garlic and crispy rosemary sprig to the platter, and drizzle with the pan juices.