Wash the livers carefully. Put in a saucepan with the onion, cover with water and bring to a boil. Simmer 20 minutes. Drain, and discard the onion.
Put the livers through a food grinder 3 times until vbery smooth, or run in an electric blender 10 to 15 seconds. Add melted butter and mix well.
Render the chicken fat until smooth and liquid. Add with salt, pepper, mace, mustard and anchovy paste to ground livers. Mix until smooth. Add the brandy, mixing well.
Place the mixture in a mold, pressing it down until firm. Chill 3 hours. Turn out on a serving platter. Slice about ¼" thick and place on thin rounds of bread of your choice. Heap high with garnishes and serve with a knife and fork.