For the mushrooms: Remove the stalk from the button mushrooms. Arrange the mushroom caps stalk side up in a roasting pan. Place in each mushroom a couple leaves of oregano, a knob of butter, a few drops of red wine vinegar and a season of salt and pepper. Cooking in a hot oven (180°C–200°C), they should take about 10–15 minutes.
Insert some aromatic bay leaf and oregano in to the rolls of the sausage, cook in a medium-hot pan until cooked through and golden brown. Allow it to rest and fry the pierogi in the sausage fat.
Serve all together with some green oil and creamy mustard (equal parts of dijon mustard and sour cream with a spoon of grainy mustard.
