Step 1

Place steak, onions, Dijon mustard, salt, pepper, dill, mushrooms and garlic in a slow cooker and stir together.

Step 2

In a mixing bowl, add the flour and then slowly whisk in the beef broth. Add to slow cooker mixture and stir together.

Step 3

Cover and cook on low for 6 to 7 hours.

Step 4

Turn slow cooker off and remove lid and let sit for 10 to 15 minutes. Stir in sour cream.

Step 5

Serve sauce on a bed of egg noodles. Garnish with fresh dill, if desired.