To brine the pork roast, put the ice in a large bowl. In a medium pot over medium heat, combine 3 cups water, the wine, 2/3 cup salt, the sugar, peppercorns, fennel seeds, thyme, ginger and garlic and bring to a simmer, stirring to dissolve the salt and sugar. 

Remove from the heat and pour the brine mixture over the ice. Let cool to 45°F on an instant-read thermometer. You should have about 8 cups brine. Place the pork loin in a large container or a brining bag and add the cooled brine, immersing the meat. Refrigerate overnight.

To roast the pork and onions, preheat the oven to 425°F (400°F if using a convection oven). 

Remove the pork from the brine, discarding the brine. Pat the pork dry with paper towels and let stand at room temperature for 30 minutes.

Rub the pork with 2 tablespoons of the olive oil and season with 2 tablespoons salt and some pepper. Place the pork, bone side down, in a roasting pan and roast for 30 minutes.

In a bowl, toss together the cipollini onions, rosemary sprigs and the remaining 1 tablespoon olive oil. 

Reduce the oven temperature to 350°F and add the onions and rosemary sprigs to the pan, scattering them around the pork loin. Continue roasting until an instant-read thermometer inserted into the center of the pork, away from the bone, registers 137°F, about 45 minutes more. 

Transfer the pork to a carving board, cover loosely with aluminum foil and let rest for 20 minutes before carving.

To serve, snip the twine and carve the pork loin into individual chops. Serve each chop with some of the pan juices and roasted onions. Garnish with rosemary leaves. Pass the chutney (recipe below) at the table.

While the pork is roasting, prepare the chutney: In a dry small fry pan over medium heat, heat the mustard seeds, moving the pan occasionally to ensure even toasting, until they are lightly toasted, fragrant and just beginning to pop, about 2 minutes. Set aside.

In a 4-quart pot over medium heat, warm the rice bran oil. Add the onions and cook, stirring occasionally, until soft, about 1 minute. Add the grapes, stir to combine and cover the pot. Cook, stirring often, until the grapes begin to wilt, 10 to 12 minutes. Add the verjus, star anise, coriander, cinnamon, raisins, salt and the toasted mustard seeds and stir well. Cook uncovered over medium heat until the liquid has reduced and the mixture is thick, 10 to 15 minutes. 

Remove from the heat and serve warm or cold. The chutney will keep in an airtight container in the refrigerator for up to 1 month.