How to Make It
Preheat the oven to 425°. On a large rimmed baking sheet, toss the rutabaga with the carrots, garlic and olive oil. Season with salt and pepper. Roast the vegetables for 35 minutes, until tender and browned in spots. Transfer to a platter; keep warm.
Meanwhile, season the roast with salt and pepper. In a large cast-iron skillet, melt the butter over moderately high heat.
Add the roast and brown it all over, about 6 minutes. Roast the meat in the oven for 20 to 25 minutes, until an instant-read thermometer inserted in the thickest part registers 120°. Transfer the roast to a carving board; let rest for 10 minutes.
Pour off all but 2 tablespoons of fat from the skillet. Add the sliced shallot and cook over moderate heat until browned. Add the red wine, bring to a boil and simmer until reduced by half. Return the sauce to a boil and whisk in the cornstarch slurry. Cook over moderately high heat until thickened. Season with salt and pepper.
Thinly slice the roast across the grain and serve with the red wine sauce and roasted vegetables.