1. Place bratwurst links in slow cooker and top with sauerkraut, apples and onion. Sprinkle with brown sugar and caraway seeds. Cover and cook on low until bratwurst reaches 165ºF on an instant-read thermometer, 3 to 4 hours.
2. Spread 1 Tbsp. mustard on each hot dog bun. Spoon some sauerkraut mixture on buns, top each with a sausage and serve.