Peel the onions and cut them into fine strips. Heat the lard or fat on medium-high heat in a large pot. When hot, add the onions and roast for 3-4 minutes until they start to brown.
Drain the sauerkraut in a sieve, pressing gently to remove excess liquid. Cut through the sauerkraut a few times with a knife. Add 600g of the sauerkraut to the onions and sauté on medium heat for 2-3 minutes. Pour in the white wine, meat broth, and the pinch of sugar.
Peel the apples and cut them into small pieces. Dice the bacon into small pieces. Add the apples and bacon to the sauerkraut and braise on medium heat for 2-3 minutes.
Reduce heat to medium-low, cover the pot, and simmer for 1 hour and 30 minutes, stirring occasionally, until the sauerkraut is very tender.
Add the remaining 300g of sauerkraut. Cover and cook on medium-low heat for 15 minutes more.