Parboil a large sweetbread and cut in eight pieces. Cook in hot frying-pan with a small quantity of butter, adding enough beef extract to give sweetbread a glazed appearance. Cut bread in slices, shape with a circular cutter three and one-half inches in diameter, and toast. Spread each piece with two tablespoons grated Parmesan cheese seasoned with salt and paprika and moistened with two tablespoons heavy cream. Arrange one piece of sweetbread on each piece of toast and season with salt and pepper. Put in individual glass-covered dishes, having two tablespoons cream in each dish. Cover each piece of sweetbread with sautéd mushroom cap, put on glass covers, and bake in a moderate oven eight minutes.