1. Wash and dry meat before cutting into thin slices.
2. Peel and finely chop onions. Wash and trim mushrooms, slice thinly and sprinkle with lemon juice.
3. Heat oil in a large, heavy-bottomed pan. Brown meat, turning until done, then remove from pan.
4. Melt butter with oil in the pan and fry onions until transparent. Add mushrooms, cover and sweat for 10 minutes.
5. Mix soured cream with cornflour and paprika.
6. Return meat to pan with mushrooms, add cream mixture and then white wine.
7. Simmer ragout gently for a few minutes.
8. Season to taste with salt and pepper.