Heat 2 Tbsp of oil in a large cast iron skillet over medium heat. Place the brussels sprouts cut side down in the pan. Allow the sprouts to slightly brown before transferring to the oven to finish, about 10 minutes. Roast in the oven for 15 minutes, remove from oven and toss well, and place back into the oven for another 10-15 minutes or until they are tender with a toasted brown color.