Preheat oven to 350°. In a large frying pan, heat 1 tbsp. oil over medium-high heat. Season pork with salt and pepper; brown lightly all over, about 5 minutes.
Transfer pork to a foil-lined 9- by 13-in. baking pan. Add remaining 1 tbsp. oil to frying pan, reduce heat to medium, and add onion. Cook, stirring, until softened, 3 minutes. Add garlic; cook 1 minute, then pour in chicken broth, cranberry sauce, rosemary, and vinegar. Cook 2 minutes.
Pour hot cranberry sauce over pork and bake, uncovered, until an instant-read thermometer inserted into meat registers 160°, about 20 minutes. Let pork rest 10 minutes, then slice and serve with sauce.
Note: Nutritional analysis is per serving.