- Melt half the butter in heavy large deep skillet over medium heat.
- Add onions and bell pepper and sauté‚ until light golden about 10 minutes.
- Add mushrooms and sauté‚ until starting to soften about 5 minutes.
- Mix in flour and paprika and stir 2 minutes.
- Mix in stock and tomato paste.
- Bring to boil stirring constantly.
- Boil until sauce thickens and paprika flavor mellows stirring frequently about 8 minutes.
- Mix in sour cream.
- Remove from heat and add dill.
- Season to taste with salt and pepper (can be prepared 1 day ahead. Cover and refrigerate. Bring to simmer before adding beef).
- Melt half of remaining butter in another heavy large skillet over medium-high heat.
- Working in batches add beef season with salt and pepper and cook until just brown on each side.
- Transfer to plate.
- Add more butter as needed.
- When all beef is brown add to sauce along with any drippings on plate.
- Add dry white wine to skillet and bring to boil scraping up any browned bits.
- Boil until syrupy about 3 minutes.
- Add to beef.
- Sprinkle with chopped tomatoes before serving if desired.