Cut beef into slices, season with salt and pepper.
Dust the slices of beef with flour.
Heat olive oil in skillet, and sear meat on both sides.
Transfer to the slow cooker.
In the same skillet add the butter. Sauté onions, garlic and mushrooms until tender. Transfer to the slow cooker.
Deglaze the skillet with red wine.
Stir in the beef broth, paprika and both mustards.
Pour over the beef and stir together.
Cook on low setting for 4-5 hours or high setting for approximately 2 hours.
Before serving, stir in the sour cream.
Garnish with fresh parley, chives or green onions.
Serve with egg noodles, broad noodles, polenta or mashed potatoes.
If you find the broth is not thick enough, ladle out ½ cup of broth. Whisk the broth together with 2 tablespoons of cornstarch. Stir into the beef and cook on high for an additional 20 minutes or until sauce thickens.