Mash eight or ten potatoes smooth with butter; salt, and work in the beaten whites of two eggs. Then fill a greased jelly-mould with the mixture, pressing it in firmly. Set aside to harden. When cold, scrape about a teacupful, or less, from the middle, leaving firm, thick walls. Fill the cavity with minced mutton, highly seasoned, mixed with crumbs moistened with gravy, and not too soft. Fit a piece of fried bread in the mouth of the filled cavity; turn out the casserole carefully upon a stone-china or block-tin dish ; wash all over with beaten egg and set in a hot oven ten minutes to heat and glaze. The mince should be very hot when it goes in and stiff enough to keep its shape.