Poke a few holes in bratwurst with a fork to allow steam to escape. Cook in half an inch of water on medium heat. Cover and leave until water evaporates. turn off heat and wait for bratwursts to cool. While waiting, peel and dice the potatoes. Slice cooled bratwursts into bite sized pieces. Combine bratwurst, potatoes and broth in wide skillet or saute pan, simmer until water evaporates and potatoes are tender (about 15 minutes). While waiting, peel and dice apples. Chop onions. Add apples and onions to pan. Push brats, apples and potatoes to one side, sprinkle sugar over a portion of skillet. Stir over high heat until sugar caramelizes (google caramelizing sugar so you know what you're doing). Add butter and stir with potatoes and apples. Sprinkle with salt and TASTE. Serve immediately.