Cook’s Note: Silver skin is a tough connective tissue found on certain cuts of beef. It doesn’t break down during the cooking process, so for best results, it should be removed with a sharp knife before cooking. Simply slide the knife under the silver skin and carefully slice it off.
Combine the oregano, parsley, thyme, garlic powder, onion powder, salt, pepper, and dry mustard in a small bowl.
Rub the spice blend evenly over the whole roast, then place it on a rimmed baking sheet or roasting pan. Set aside at room temperature for 20 to 30 minutes to allow the spice mixture to adhere to the roast.
Preheat the oven to 450°F (230°C). Roast for 15 minutes, then reduce heat to 325°F (170°C). Continue to roast for 12 to15 minutes per pound, or until the internal temperature reaches 125°F (52°C) for rare (this accounts for carryover cooking). The exact cooking time will depend on the size of your roast and desired degree of doneness. Use a meat thermometer to get it just right.
Allow to rest for 10 to 15 minutes before slicing.
For Sauteed Mushrooms:
Heat a large skillet over medium heat. Add the mushrooms to the dry skillet. Cook over medium heat for 10 to 15 minutes, stirring periodically, until the mushrooms brown, become fragrant, and reduce in size by about half.
Reduce the heat to low and add the butter and thyme. Stir until the butter is melted and well combined with the mushrooms. Add the sherry, if using, right before serving.
These mushrooms can be stored in the refrigerator for up to 5 days.