- In a large 24-cup (6 litre) pot, bring 2 cups (500 ml) of the water, the salt and brown sugar to a boil. Stir just until the brown sugar has dissolved. Remove from the heat. Add the pepper, bay leaves and remaining water. Place the turkey roast in the brine. Weigh the roast down with a plate to keep it completely submerged. Refrigerate for 12 hours.
- In a pot of salted boiling water, blanch the white part of the leek for 2 minutes. Add the green parts of the leek and cook another 2 minutes. Drain and plunge in a bowl of ice water. Pat dry with paper towel. Set the green parts aside for the sauce and the white part aside for the turkey.
- With the rack in the middle position, preheat the oven to 400°F (200°C).
- Remove the turkey from the brine and pat dry with paper towel. On a work surface, unroll the roast and lay it flat, skin side down. Remove the cutlets and keep for another use. Line the inside of the roast with the ham slices. Place the white part of the leek along the lower third of the roast. Starting with the leek end, tightly roll the roast. Slide several strands of butcher’s twine under the meat, letting them extend out on either side. Tie the roast and cut the excess twine.
- In a large ovenproof skillet over medium heat, brown the roast on all sides in the butter, regularly basting the meat with the hot butter. Transfer to the oven and cook for 1 hour 15 minutes or until a meat thermometer inserted in the centre of the roast reads 165°F (74°C).
- Remove the roast from the oven and set aside on a plate. Tent with foil and let rest for 10 minutes.
Cheesy Béchamel Sauce
- Meanwhile, in a pot over medium heat, soften the shallot and garlic in the butter until tender. Add the flour and cook 1 minute while stirring with a whisk. Gradually add the milk and bring to a boil, whisking constantly. Add the cheese and stir until completely melted. Add the nutmeg and green parts of the leek. Season with salt and pepper.
- Remove the twine from the roast. Slice the roast and serve with the sauce and steamed asparagus, if desired.