Heat butter in a heavy pot or Dutch oven over medium heat.
Add beef chunks and brown on all sides, working in batches if needed.
Add sliced onion and sauté until soft and slightly golden.
Pour in beef broth and red wine vinegar, then add allspice and bay leaves.
Season with salt and pepper, bring to a gentle simmer, then cover and cook on low for 1½–2 hours, until the beef is tender.
Add rättika or kålrabbi cubes and cook for another 20–25 minutes until soft.
Remove lid and simmer uncovered for 10 minutes to reduce and thicken the sauce slightly.
Optional: whisk in a small pinch of xanthan gum or heavy cream if you prefer a creamier texture.
Taste and adjust seasoning before serving.