Step 1

Preheat oven to 500°. Coarsely grind bay leaves, peppercorns, coriander seeds, and fennel seeds in a spice mill, mortar and pestle, or blender. Transfer spice mixture to a small bowl and mix in rosemary, kosher salt, and 2 Tbsp. oil.

Step 2

Using a sharp knife, score fat cap in a crosshatch pattern, spacing cuts about ½" apart and avoiding cutting into flesh. Rub spice mixture all over pork, making sure to work it into the cuts. Set pork on a wire rack set inside a roasting pan.

Step 3

Toss onions, garlic, and remaining 1 Tbsp. oil in a medium bowl to coat, then scatter around pork. Roast in oven until skin begins to puff and crisp, about 30 minutes. Remove roast from oven and reduce oven temperature to 350°. Pour wine and 1 cup water into pan and return to oven. Roast until an instant-read thermometer inserted into the center of roast registers 150°, 45–75 minutes (time will vary depending on how thick your roast is). Let rest at least 30 minutes and up to 2 hours before carving.

Step 4

Sprinkle roast with sea salt and serve with any pan juices spooned over.

Step 5

Do Ahead: Pork can be rubbed with spice mixture 2 days ahead. Cover; chill.