Pour a thin layer of the paste in 2 baking tins and bake in a moderate oven till the paste has risen about ½ an inch and is slightly browned. Remove the paste from the tins, and cover one sheet of pastry with the Béchamel, to which grated cheese and shredded mushrooms have been added. Cover with the other sheet of pastry, and divide into rectangular pieces, about 3 inches long and just under 1 inch wide. Coat these with Béchamel, next dip in fine breadcrumbs, then in flour. Coat with beaten yolk of egg, again dip in fine breadcrumbs, and fry in boiling fat.