Let the slow cooker do the Sunday work. Beef stroganoff over egg noodles gets impossibly tender and creamy after hours of simmering — worth every calorie.
Pat beef chuck roast dry and cut into 2-inch cubes. Season generously with salt and black pepper.
Melt butter in a large skillet over medium-high heat. Brown beef cubes in batches, making sure to sear all sides well. Transfer browned beef to the slow cooker.
To the same skillet, add sliced onions and mushrooms. Sauté over medium heat until the onions are golden and the mushrooms release moisture, about 6 minutes.
Sprinkle flour over the onion-mushroom mixture and stir continuously for 2 minutes to form a roux. Add Dijon mustard and Worcestershire sauce, stir, then pour in beef broth to deglaze, scraping any browned bits.
Pour the vegetable-broth mixture over the beef in the slow cooker. Cover and cook on LOW for 6-8 hours, until beef is fork-tender.
Thirty minutes before serving, cook egg noodles according to package instructions. Drain and set aside.
When the beef is done, turn the slow cooker to WARM. Stir in sour cream until smooth and creamy. Check seasoning and adjust salt and pepper if needed.
Serve stroganoff over egg noodles, spooning plenty of sauce on top. Garnish with extra black pepper if desired.