Preheat oven to 350ºF.

Tie the roast and season generously with salt and pepper.

Mix together rosemary and garlic. Add 2 tablespoons of olive oil and stir to combine, creating a paste. Reserve.

In a cast iron skillet, over medium heat, heat the vegetable oil and, once smoking hot, sear all sides of the meat, about 5-8 minutes.

Remove skillet from heat. Brush the herb-garlic mixture all over the roast.

Bring the roast, in the cast iron skillet, to the preheated oven and cook for about 1 to 1.5 hours or until a meat thermometer reads 135F degrees (medium-rare). Let it rest for at least 10 minutes before serving (final temperature should be 145F for medium rare).

While the roast is resting, sauté the mushrooms over medium heat with 2 tablespoons butter until cooked through and no liquid is left in the pan, about 5 minutes. Season with salt and pepper.

Remove roast from the cast iron skillet and bring the skillet to the stovetop. Add stock to the pan and deglaze the pan, scraping all the bits from the bottom. Allow to simmer until thick.

Add the mushrooms to the sauce, stir in the remaining 2 tablespoons of butter and stir until the sauce is silky. Then, place the roast back in the cast iron with the sauce and spoon some of the sauce over the roast.

Garnish serving platter with fresh rosemary if desired.