Cut along 1 side of the breastbone, and then down along the ribs; gently pull and cut the meat away from the bone to cut the breast off the carcass. Do the same to remove the other breast.
Season the turkey breasts on both sides with a generous amount of salt and pepper. Put a large roasting pan on the stove over medium heat and get it good and hot. Drizzle the pan with a 3-count of oil. Add a few sage leaves and stir to flavor the oil. Lay the breasts in the hot oil, skin-side down and cook for about 5 minutes until the skin begins to set and crisp. Flip the breasts over and push them off to 1 side.
Add the shallots, carrots, and handful of sage leaves to the pan and stir to coat with the oil. Sprinkle the vegetables with salt and pepper. Stick the pan in the hot oven and roast for about 30 minutes until the internal temperature of the turkey reaches 160 degrees F on an instant read thermometer, and the shallots and carrots are tender and browned.
Remove the turkey and the vegetables to a serving platter and set aside. Now work on the gravy: Put the roasting pan over 2 burners, over medium heat. Stir in the flour with a wooden spoon. Then gradually stir in the stock, scraping the bottom of the pan to pick up all of the browned bits. Give the gravy a squeeze of lemon and season, to taste, with salt and pepper. Slice the turkey and serve with the gravy.