Cream of Asparagus and Mushrooms

Preparation:

Preparation: Season the sliced mushrooms with 10 g of butter and 2 tablespoons of oil, salt and pepper. Melt 20 g of butter, mix in 1 tablespoon of flour and dilute, little by little, with 3/4 of a liter of boiling water, stirring constantly. Season with salt and pepper, add the asparagus pieces and continue cooking for 35 minutes. Mix everything, put it back on the heat, add the mushrooms and cook for 5 minutes, add the beaten egg yolk and the parmesan.