In a large frying pan on high heat add kielbasa until the bottom side is seared. Then flip pieces to sear the other side. About 3 min each side. Set aside.
In the same pan, Reduce the heat to low and add in the butter and onion to cook until the onion becomes translucent.
Add shredded carrots and cook for another 6 minutes.
Add sauerkraut to the pan. Mix well and then cover the pan for an additional 35 mins. If the sauerkraut is browning too fast, add some additional water to the pan.