Preheat the oven to 350 degrees.

Heat 2 tablespoons olive oil in a medium (10 to 11-inch) sauté pan over medium heat. Add the onion and fennel seeds and cook for 6 to 8 minutes, tossing occasionally, until the onion is tender. Add the garlic and cook for one minute. Off the heat, add the chopped sage and the rosemary and set aside to cool.

Meanwhile, open the turkey breast on a cutting board, skin side down. Sprinkle the meat with 4 teaspoons salt and 1½ teaspoons pepper.

When the onion mixture is cool, spread it evenly on the meat. Grate the butter and sprinkle it on top. Arrange the prosciutto on top to totally cover the meat and filling.

Starting at one long end of the turkey breast, roll the meat up jelly-roll style to make a compact cylindrical roulade, ending with the seam side down. Tie the roulade tightly with kitchen twine at 2 to 2½-inch intervals to ensure that it will roast evenly. Slip the whole sage leaves under the twine down the center of the roulade.

Place the roulade, seam side down, in a roasting pan and pat the skin dry with paper towels. Brush the skin with 2 tablespoons olive oil and sprinkle with 1 teaspoon salt and ½ teaspoon pepper. Pour the wine and 1 cup of water in the roasting pan (not over the turkey). Roast for 1½ to 1¾ hours, until the skin is golden brown and the internal temperature is 150 degrees. Remove from the oven, cover with foil, and allow to rest for 15 minutes. Remove the string, slice crosswise in ½-inch-thick slices, and serve warm with the pan juices.