Melt the butter in a large Dutch oven or heavy-bottomed pot over medium-high heat. Pat the beef cubes dry with paper towels and season them generously with salt and black pepper.

Add the beef to the pot in batches, searing until deeply browned on all sides, about 8 to 10 minutes total. Remove the beef with a slotted spoon and set it aside on a plate.

Reduce the heat to medium, add the chopped onions to the remaining fat in the pot, and cook for 5 minutes until soft and translucent. Sprinkle the flour over the onions and stir constantly for 2 minutes to cook out the raw flour taste.

Slowly pour in the beef broth while whisking continuously to scrape up any browned bits from the bottom of the pot. Return the seared beef and any accumulated juices back to the pot, then add the bay leaf.

Bring the liquid to a boil, then reduce the heat to low, cover with a tight-fitting lid, and let it simmer gently for 45 minutes until the beef begins to tenderize.

Stir in the cubed potatoes, carrots, and rutabaga, ensuring they are mostly submerged in the gravy. Cover and cook for another 35 to 40 minutes, stirring occasionally, until the vegetables are fork-tender and the potatoes have slightly broken down to naturally thicken the stew.

Discard the bay leaf, taste the stew, and adjust the seasoning with additional salt and pepper if needed. Ladle the hot Brun Lapskaus into deep bowls, garnish with fresh parsley, and serve alongside traditional Norwegian flatbread and pickled beets.