Let the butter get hot in a pan and fry the meat vigorously. Put the meat on a plate and keep it warm.
Dice the onion and fry in the pan until translucent. Deglaze the roasting mixture with wine and let the wine boil down a little, loosening the roasting mixture from the bottom, stir in the tomato paste. Add the stock, green pepper and cream and bring to the boil. Stir the sauce well with a magic wand. Add the meat again and let it steep. Season to taste with salt and pepper.