Prep the goose (refer to the link above how to do that). The most important steps are: remove the bag with innards, remove the fat around the bottom, remove the oil gland in the tail, and remove any remaining feathers and quills. The let it sit at room temperature while you prep the stuffing. It should not go directly from the fridge into the oven. That will extend the cooking time.Save the innards, fat and anything you cut off for the sauce! For the stuffing, dice the toast, apples, celery and onions.
Heat oil in a pan on meduim heat and add the onions. Let them slowly brown for about 10 minutes. Add the bacon bits and cook for another 5 minutes until the bacon has browned as well. Press the garlic and wait approximately 1 minute until fragrant. It should not get dark. Add chestnuts, celery, and apples, and after another 2-3 minutes, add the toast. Roast for another 5 minutes.
Add the chicken stock in parts. The toast should soak up the liquid without the stuffing getting watery. Add salt and pepper to taste (don't underseason!).
Take off the stove and let cool.
Season the goose with salt on the outside and inside.
Preheat the oven to 220℃ (430℉) top/bottom heat.
Sow the neck side of the goose shut (or if you don't have cooking yarn, like me, use tooth picks in a zigzag manner). Add the stuffing to the goose (it should be packed) and then also sow the bottom side shut (or again, use toothpicks). If you want to be on the safe side, add a cooking thermometer to the goose. It should go into the thigh without touching the bone.
Put the goose onto an oven rack, and place the rack on top of a dripping pan/deep baking tray. Don't skip this, otherwise you will have goose fat all over your oven!
Put the goose in the oven and roast for 1 hour.
Lower the oven temperature to 80℃ (180℉). Make sure that your oven actually reaches this temperature! I actually have to set my oven to 90-100℃. I use my second thermometer to check on this throughout the day.
Keep in the oven at this temperature for 8 hours. If your goose is heavier or lighter, the time will vary. A 4 kg goose will take approximately 7 hours, a 6 kg goose approximately 9 hours.
If you or your guests are running late, that's ok. Just keep the goose in the oven for a bit longer. The low temperature means your goose will not dry out.
30 minutes before dinner, increase the heat to 180℃ (360℉) and roast for another 30 minutes. If you are not happy with the crispyness of the skin after about 20 minutes, you can also turn on your oven grill. But then you need to have a close eye on it to avoid burning it!
Finally, take out of the oven, carve, and serve with sides.
