While the meatballs bake, melt the butter in a large skillet over medium heat.
Add the onion and cook it for about 5 minutes, stirring occasionally, until it's soft and just beginning to brown.
Add the cabbage to the skillet. Continue cooking and stirring for about 5 minutes more, until the cabbage begins to soften up.
Clear a spot near the center of the skillet and add the garlic. Cook it for about 1 minute, until very fragrant, then stir the garlic into the cabbage mixture.
Sprinkle the flour into the skillet and stir to coat the cabbage with the flour. Continue cooking and stirring the cabbage for about 2 minutes.
Add the coconut milk and broth, a bit at a time, stirring well between each addition. Then stir in the mustard.
Bring the liquid up to a simmer and cook everything for about 10 minutes, or until the sauce thickens and the cabbage is tender. Stir the mixture occasionally as it simmers.
Stir in the sauerkraut and remove the skillet from the heat.
Tastes-test the cabbage and season it with salt and pepper to taste.
Divide the cabbage onto plates and top it with the meatballs. Sprinkle with chives and serve.