Melt the butter in an ovenproof skillet over medium-high heat. Brown the pork tenderloins in the skillet, then transfer to a plate and set aside. Use the same skillet to sauté the onion and garlic over medium heat. When golden brown, add the cranberries, honey, and chicken stock to the skillet. Bring to a boil, and scrape the bottom of the skillet to release any browned bits into the sauce. Return the tenderloins to the skillet. Place in the oven and roast for 15-20 minutes, until a meat thermometer reads 140˚F-145˚F in the thickest part of the meat, being careful not to overcook.