In a skillet, heat the oil. Season the roast with salt and pepper and sear on all sides over moderately high heat; transfer to a roasting pan.
Add the wine to the skillet and boil for about 3 minutes, scraping up the browned bits. Add the wine, broth and water to the roasting pan and bring to a boil. Add the onion, garlic, carrots, fennel, and bay leaf. Cover and braise in the oven until the fennel is tender, about 1 hour; transfer the fennel to a baking dish and cover.
Return the roast to the oven; cook until the roast is tender and an instant read thermometer inserted in the thickest part registers 180 degrees, about 1 hour longer.
Discard the onion and bay leaf. Transfer roast and carrots to the baking dish with the fennel. Cover and keep warm in the oven. Strain the cooking liquid into a saucepan, pressing to mash the garlic. Boil until reduced to 1 1/2 cups, about 25 minutes. Season with salt and pepper.
Transfer the roast to a carving board and remove the strings. Cut into 4 thick slices and transfer to plates with the carrots and fennel. Pass the sauce at the table.