Trim fat from roast and cut against the grain into thin slices. Season the beef with salt and pepper.
Combine beef, onions, garlic, dried mushrooms, dill, Dijon mustard and parsley in a slow cooker. Stir.
Measure flour into a separate bowl or measuring cup, and slowly add beef broth, whisking until incorporated.
Pour broth mixture into the slow cooker and stir.
Cover and cook on high for 1 hour.
After 1 hour, remove the lid and stir the beef stroganoff. Lower the heat to low and cook for 4 more hours.
Once cooking time is complete, turn off the slow cooker and remove the lid. Let stand for 10 minutes
Boil water on stovetop and cook the egg noodles, according to the package directions. Drain in a colander.
After the beef stroganoff has cooled slightly, uncovered, for 10 minutes, add sour cream to the slow cooker and stir well.
Serve beef stroganoff over egg noodles and garnish with fresh parsley, if you like.