Cut the beef into large cubes.
Dip in flour and fry in vegetable oil.
Add coarsely chopped champignons, salt and pepper to taste.
When the meat and mushrooms are ready, add 1/2 cup of wine and evaporate.
Transfer everything to a slow cooker adding garlic, tomato paste and mustard.
Cook on simmer for 60 minutes. At the end add 3 tablespoons of sour cream and stir.
Transfer to a ceramic pot and serve. Garnish with herbs when serving.