Prepare beet kvass in advance or buy it at the store. Wash the beets, peel and cut into large cubes. Peel the onion and chop finely. Cut the pork into pieces.
Place the chopped beets in a ceramic pan and cover with millet.
Fry the pieces of pork, first rolling them in flour, on both sides until golden brown. Place the fried meat on the beets with millet.
Place the onion in the pan where the pork was fried and fry it a little. Add pork. Fill everything with kvass and place in the oven, preheated to 220 °C, for 45-50 minutes.
Serve the pork and beets slightly cooled with black bread and sour cream.