Ask your butcher to remove the chine bones from the rib roasts. The meat needs to brine for two days.Plus: Ultimate Holiday Guide Centerpiece Roasts
In a very large pot, combine the water, salt and sugar; stir to dissolve the salt and sugar. Totally submerge the roasts in the brine and refrigerate for 2 days.
In a medium saucepan, combine the orange zest and juice with the shallots and ginger and boil over moderate heat until almost syrupy, about 20 minutes. Whisk in the mustard, tomato paste and 2 tablespoons of the whisky and simmer for 5 minutes. Remove from the heat and stir in the remaining 2 tablespoons of whisky. Season with salt and pepper and let cool.
Preheat the oven to 375#176;. Remove the roasts from the brine and pat dry. In each of 2 very large skillets, heat 2 tablespoons of the oil until shimmering. Add the roasts, meaty side down, and brown on all sides over moderately high heat, about 15 minutes. Set the roasts in a large roasting pan, meaty side down.
Spread 1/4 cup of the glaze on the rib side of each roast. Roast the pork in the center of the oven for 30 minutes. Turn the roasts and spread the remaining glaze over them. Roast for 1 hour longer, or until the pork is deeply browned and an instant-read thermometer inserted in the thickest part registers 150°. Transfer the roasts to a carving board and let rest for 15 minutes. Carve the roasts between the ribs and serve.
The glaze can be refrigerated for up to 5 days.