Pan Seared Roast With Cremini Mushrooms And Red Onions

"I love finding little gems like this roast, priced for quick sale... must be the wee bit of Scottish from my mother's side?Seasoned and seared in the cast iron, then roasted on top of red onions and finished with butter, thyme and cremini mushrooms. #Delicious"
-- @zimmysnook

Recipe Intro From zimmysnook

This beautiful one-pan dish is a must for entertaining. Everything @zimmysnook creates is fantastic. This robust beef roast, surrounded by juicy mushrooms, is a winner. Perfectly prepared with mashed potatoes, serve with broccolini and follow with a poached pear with creme anglaise and your guests will leave sated and impressed.

1 (3-pound) beef roast, trimmed of excess fat (inside round)
Kosher salt
Freshly ground black pepper or a premixed steak seasoning of your choice
3 tablespoons olive oil
6 ounces sliced cremini mushrooms
2 or 3 - 1/2 slices of red onion
4 tablespoons butter
6 sprigs of fresh thyme

Preheat the convection oven to 325F or 350F for non-convection.

Season beef liberally with salt and pepper or steak seasoning. Heat the oil in a large cast iron skillet, over medium-high heat, until very hot but not smoking. Add the meat and sear on all sides. About 1.5 minutes per side.

Remove the skillet from the heat and place the onions slices on the pan directly under the roast. Put the skillet in the oven and roast for 30 minutes. Add the mushrooms, butter and thyme to the skillet around the roast.

Continue to roast until an instant-read thermometer registers 130 F, about another 15-20 minutes. Toss the mushrooms butter and thyme each time when checking the temperature and bast the the roast with butter/drippings in the bottom of the pan.

Let roast rest for 10 minutes before slicing and serve with the mushrooms/onions and any liquid left in the pan.