1. Peel potatoes and cut into quarters. Cover with water. Bring to a boil and boil until tender, about 15 minutes.
2. Cut apple into quarters and remove core. Slice into 1/4 inch slices and then cut into matchsticks. Peel and thinly slice red onion.
3. To a sided skillet with a lid, add chicken broth, reserving 1/4 cup (per 4 servings) for later. Add celery seed and mustard. Whisk to combine.
4. Add in brats and bring to a boil. Turn down to a simmer, cover, and cook for 10 minutes.
5. Remove lid and cook for 7 more minutes, or until sausages are cooked through.
6. Liquid will reduce to almost nothing but you may add small amounts of water to keep mixture from burning to bottom of skillet. You don't want the pan to get completely dry.
7. While sausages cook, mash potatoes.
8. Drain potatoes, return to hot pot, and add olive oil, coconut milk, salt, pepper, and nutmeg.
9. Using a hand mixer or potato masher, mash until creamy and smooth. Taste and adjust seasoning to your liking.
10. When sausages are done, remove from skillet. Add in sauerkraut, apple, red onion, and reserved chicken broth.
11. Cook for 5 minutes, being sure to scrape up all the flavor from the bottom of the skillet. Cook until warmed through and apples are tender-crisp.
12. To serve, place mashed potatoes on serving platter. Top with apple sauerkraut. Place bratwursts on top and serve with mustard alongside.