Soak the bun. Knead together with the mince, egg, mustard and onion. Spice up. Shape 8 medallions and wrap each one with 1 slice of bacon. Fry for about 10 minutes on both sides.
Cut the remaining bacon into slices and fry until crispy. Add the mushrooms and shallots and sauté. Deglaze with stock and white wine, bring to the boil. Add the cream and simmer for a few minutes. Stir starch and 1 tablespoon water until smooth and bind the sauce with it. Season to taste with salt and pepper.