Kat Can Cook

0 Remove the Beef from the fridge an hour before cooking so it reaches room temperature.
3 Pat dry with a paper towel and rub all over with oil. Season all over with 3 teaspoons of salt, 1 teaspoon dried thyme, 1 teaspoon onion powder, and ½ teaspoon fresh cracked pepper. Set aside for an hour at room temperature.
1 Preheat the oven to 325 F.
2 Transfer the seasoned beef to a cast iron pan, fat side up, and roast for about an hour or until the internal temperature reads 135 for medium rare (that’s how we like it cooked).
4 Remove the beef from oven when done, using tongs to set the beef on a cutting board to rest for at least 20 minutes to allow the juices to redistribute.  
5 Without wiping out the pan, bring the same pan you cooked the beef in to warm back up over medium heat.
6 Add the sliced onion and a big pinch of salt to the pan and cook, stirring periodically, for 15-20 minutes. Halfway through, add a splash of water to the pan and use a wooden spoon to scrape up any bits leftover from the beef… don’t leave that flavor behind!
7 When the onions are done they will be soft and deeply browned from the pan’s seasoning.  Remove from heat.
8 While the beef rests, whisk the horseradish and mayonnaise in a small bowl and set aside for serving
9 Assemble the sandwiches by spreading a generous layer of horseradish mayonnaise over bread roll bottoms. Add a big scoop of sautéed onions before dividing the sliced roast beef and distributing it evenly on the onions. I suggest adding a Grillo pickle on top of the beef, put the top on the sandwiches and cut in half.  Warning- will be messy!
11 Serve and enjoy!