How to make
Wash and cut the mushrooms into slices. Put them in a pot with a liter of water, salt and boil them for 10 minutes.
Put the butter in another pot, pour the olive oil and when the fat has heated up, pour 2 tbsp. of flour. Start mixing right away. Fry the flour, until it aquires a golden color.
Discard the water, in which you boiled the mushrooms and stir with a wire whisk, until the mixture is homogenized and the desired thickness of the fricassee is obtained. It should be a bit thinner than boza. Add the mushrooms.
Beat the yolk with 2 tbsp. of yoghurt. Add the thickener and stir vigorously for another 5 minutes, until the yolk is pasteurized.
Remove the pan from the heat. Season with black pepper, chopped parsley and a few drops of lemon juice.
Note: it is very important to fry the flour well, otherwise the mushroom fricassee will have the unpleasant taste of raw flour!