Grind fennel seeds and black peppercorns using a spice grinder or mortar and pestle until finely ground.
In a food processor, combine the ground spices, rosemary, sage, thyme, garlic, and kosher salt. Pulse until finely chopped.
Add olive oil and pulse to form a coarse paste.
Prepare the Turkey:
Remove the skin from the turkey breast in one piece and set it aside.
Debone the turkey breast halves, removing tenderloins, and butterfly them to an even thickness.
Rub the herb paste evenly over all sides of the turkey meat.
Reassemble the breast halves into a cylindrical shape and wrap the reserved skin around the meat.
Tie the roast securely with butcher’s twine at 1-inch intervals.
Season and Rest:
Sprinkle the exterior of the roast with additional kosher salt.
Place the roast on a wire rack set in a rimmed baking sheet.
Refrigerate, uncovered, for at least 8 hours or up to 24 hours to allow the flavors to meld and the skin to dry slightly.
Roast the Turkey Porchetta:
Preheat the oven to 275°F (135°C).
Brush the roast with melted butter.
Roast until the internal temperature reaches 145°F (63°C), approximately 2 to 2½ hours.
Increase the oven temperature to 500°F (260°C) and continue roasting until the skin is crisp and the internal temperature reaches 160°F (71°C), about 15 minutes more.
Rest and Serve:
Remove the roast from the oven and let it rest for 30 minutes.
Remove the twine, slice, and serve.
More Details
Flavor Variations: Incorporate lemon zest into the herb paste for a citrusy note.
Crispier Skin: Ensuring the skin is dry before roasting helps achieve a crisp texture.
Serving Suggestion: Pair with roasted vegetables and a light gravy made from the pan drippings.