Step 1

Put the pork on a rimmed baking sheet and sprinkle all over with 1 tablespoon salt and several grinds of pepper; set aside.

Step 2

Put the fennel, allspice, whole peppercorns and juniper berries in a small skillet over medium heat and cook until the fennel begins to turn slightly golden, about 5 minutes.

Step 3

Transfer the toasted spices to a blender, add the bay leaf and blend until coarsely ground. Add the olive oil and 1 tablespoon salt and process until a coarse paste forms, about 1 minute. Spread the paste over the pork, making sure to get it into all the nooks and crannies; use a spatula to scrape up all the paste from the blender. Cover the pork with plastic wrap and refrigerate at least 8 hours and up to 24 hours.

Step 4

When ready to cook the pork, preheat the oven to 450 degrees F.

Step 5

Put the pork on a rack set in a large roasting pan and cook for 20 minutes. Lower the oven temperature to 350 degrees F and continue to cook until an instant-read thermometer registers 135 degrees F, about another 1 1/2 hours.

Step 6

Meanwhile, combine the sugar, sage, thyme, apples, onions and 6 tablespoons of the butter in a large bowl until well coated. Heat a large skillet over high heat until very hot, about 3 minutes. Add half of the apple and onion mixture and cook, stirring occasionally, until the apples and onions are dark golden all over but the apples are still firm, 2 to 3 minutes. Transfer to a rimmed baking sheet and spread into a single layer to cool, using a heatproof spatula to scrape all the remaining sugar from the skillet over the apples and onions. Repeat with the remaining apple and onion mixture.

Step 7

Return the skillet to high heat and add the wine. Cook until syrupy and reduced to about 2 tablespoons, about 4 minutes. Add the cider and cook until thickened and glossy, about 8 minutes; you should have about 1/3 cup of glaze. Swirl in the remaining 2 tablespoons butter and set aside.

Step 8

Once the pork reaches 135 degrees F, increase the oven temperature to 450 degrees F and brush the pork all over with half the glaze. Return to the oven and cook for 5 minutes. Brush with the remaining glaze and continue to cook until the internal temperature registers 145 degrees F, about another 5 minutes. Transfer to a serving platter and let rest for 30 minutes. Serve with the apples and onions.