Place the peeled and quartered potatoes in a large pot. Cover with cold water and add a pinch of salt. Bring to a boil and cook for about 20 minutes, or until the potatoes are tender and easily pierced with a fork.
1.5 kg Potatoes
While the potatoes are cooking, prepare the kale. Wash the kale thoroughly and chop it into small pieces. If you're using an onion, chop it finely as well.
1.5 kg Potatoes
Add the chopped kale (and onion, if using) to a separate pot with a little water (about 1/4 cup). Cover and cook over medium heat for about 15 minutes, or until the kale is tender.
1.5 kg Potatoes
While the potatoes and kale are cooking, prepare the smoked sausage. Place the smoked sausage in a pot of simmering water for about 10 minutes, or until heated through. Don't boil vigorously, as this can cause the sausage to burst.
1.5 kg Potatoes
Once the potatoes are cooked, drain them well. Return the potatoes to the pot and mash them until smooth. Add the milk and butter and continue mashing until the mixture is creamy and well combined. Season with salt and pepper to taste.
1.5 kg Potatoes
Add the cooked kale (and onion, if using) to the mashed potatoes. Stir well to combine everything evenly. Taste and adjust the seasoning as needed.
1.5 kg Potatoes
Serve the Stamppot Boerenkool hot, with the smoked sausage on top. Optionally, serve with mustard or piccalilli.