Drain the sauerkraut (rinse if you want a milder flavor) add to the slow cooker.
Add the yellow onion and cut kielbasa.
Add the dijon mustard, brown sugar, garlic powder, black pepper, and caraway seeds. Add the butter, you can just add it in slices. Pour over beer and stir.
Cover and cook on HIGH for 2 hours or low for 4 hours.
Video
Notes
Add any leftovers to an airtight container and keep them in the refrigerator. It is good for up to 5 days.
If you don't want to use beer, opt-in for water, chicken broth, or even apple juice.
You can substitute beef sausage for the pork kielbasa and still have great results.