Preheat oven to 425 degrees. Heat oil in a large ovenproof skillet over medium-high heat until hot but not smoking. Add pork and halved shallots to skillet. Brown pork on all sides, turning occasionally,
6 to 8 minutes. Remove skillet from heat.
Brush pork in skillet with half the jam; drizzle 2 tablespoons broth over shallots. Transfer skillet to oven. Roast, turning shallots occasionally, until an instant-read thermometer inserted into center of pork registers 155 degrees, 30 to 35 minutes.
Remove skillet from oven. Using tongs, transfer pork and shallots to a plate. Let pork rest (it will continue to cook; temperature should reach 160 degrees).
Place skillet over medium-high heat; add remaining chopped shallots. Sprinkle with salt; add remaining jam and 6 tablespoons broth. Deglaze skillet, scraping up browned bits with a wooden spoon; add cranberries, vinegar, and pepper. Cook, stirring, until berries are juicy, about 5 minutes. Stir in chopped thyme.
Slice pork; divide among plates. Garnish with thyme sprigs, if desired. Serve with cranberry pan sauce and shallots.