Preheat oven to 450 degrees F. Lightly oil a baking sheet or coat with nonstick spray.

In a large pot of boiling salted water, cook potatoes until just tender and parboiled, about 3-5 minutes; drain well. Return to pot and cook on low heat, stirring often, until potatoes are very dry.

Place potatoes in a single layer onto the prepared baking sheet. Add 2 tablespoons butter and rosemary; season with salt and pepper, to taste. Gently toss to combine.

Place into oven and bake for 20-25 minutes, or until golden brown and crisp, stirring halfway.

Place a cast iron skillet in the oven.

Using paper towels, pat both sides of the steak dry; season with Montreal steak seasoning. Remove skillet from the oven and heat over medium high heat.

Melt remaining 2 tablespoons butter. Place the steaks in the middle of the skillet and cook until a dark crust has formed, about 4-6 minutes. Using tongs, flip, and cook for an additional 3-4 minutes, or until desired doneness. Let rest 5 minutes.

Serve immediately with potatoes, garnished with rosemary, if desired.