In a skillet over medium heat, brown the bratwurst, breaking it up with a wooden spatula. Add the diced onion and cook until softened. Once fully cooked, set the mixture aside to cool.
In a mixing bowl, combine the sauerkraut, breadcrumbs, parsley, cream cheese, salt, pepper, garlic powder, and the cooled bratwurst and onion mixture. Mix thoroughly until well combined.
Form the mixture into golf ball-sized balls. Place on a baking sheet and refrigerate for 30 minutes to firm up.
Set up a breading station with one bowl of flour, one bowl of beaten eggs mixed with beer (or water/milk), and one bowl of Panko breadcrumbs.
To deep fry: In a deep frying pan, heat oil to 350°F. Dredge each sauerkraut ball in flour, then egg wash, and finally roll in breadcrumbs. Fry a few at a time until golden brown. Drain on paper towels. Serve immediately.
To bake: Preheat oven to 375°F. Dredge each sauerkraut ball as described above. Arrange on a parchment-lined baking sheet and bake for 20 minutes. Serve immediately.