In a large bowl, use a hand mixer to combine the sausage, sauerkraut, onion, parsley, mustard, and two tablespoons bread crumbs. Mix well then cover and chill for one hour.
Prepare three separate bowls for dredging. In one bowl, whisk together the egg and milk. In a separate bowl, add the flour and in the third bowl, add the bread crumbs.
Heat the vegetable oil in a shallow pot over medium high heat OR preheat heat a deep fryer to 350 F.
Use a tablespoon or measuring spoon to measure out 1-2 tablespoons of the sauerkraut and sausage mixture. Roll the mixture into tight balls about 1 inch round.
Begin dredging the sauerkraut balls by first rolling each ball first in the flour, then in the egg (let the excess drip off), then into the bread crumbs. Repeat until the sauerkraut balls have a thick breading.
Working in batches, fry the sauerkraut balls 3-5 at a time. Do not overcrowd. Cook for 5-6 minutes, flipping halfway for even browning. Continue to cook until the sausage is cooked through and the internal temperature of each ball is 160 F. Cooking times may vary.
Serve the sauerkraut balls hot with a side of plain Greek yogurt. Sprinkle on parsley for a pop of color, as desired. Enjoy!
Freeze any remaining sauerkraut balls in an airtight baggie for up to 6 months - to reheat, thaw and cook at 350 F for 15-20 minutes.