1. Cut leeks down center and clean thoroughly. Blanch and refresh. Dry very well.
2. Bake carrots, sweet potatoes, chicken fat or margarine, brown sugar, cider, salt, pepper, lemon juice and cinnamon in 375-degree oven for about 1 hour, until vegetables are tender. Puree in food processor. Cool.
3. Sweat onions in covered pan with 3 tablespoons vegetable oil, cooking slowly until onions are translucent, about 20 minutes. Puree and adjust the consistency by adding about 1 cup water until mixture is like whipped cream.
4. When carrot-sweet potato mixture is cool, add 3 eggs and 1 cup of onion puree. Set aside.
5. Boil the potatoes for about 20 minutes and then mash. Add remaining onion puree, salt and pepper. When cool, add 3 eggs and mix well.
6. Heat prunes in about 1-inch of water for 5 minutes. Drain and puree.
7. Blanch and refresh asparagus. Dry well.
8. Spray 2 loaf pans with Pam. Lay leeks across pans to line the bottom and up the sides. Be sure to leave enough leeks hanging over side to cover the top.
9. Assembly: Put in ¼ sweet potato mixture on bottom. Bury 4 asparagus in sweet potato mixture. Spread a thin layer of prune puree on top. Atop prunes, place a layer of mashed potato mixture. Cover with ¼ sweet potato mixture and repeat the same thing for second terrine. Seal the tops by folding leeks over top. Cover with foil and poke holes in top.
10. Bake in water bath for 1 hour at 375-degrees. Cool completely in water bath and chill overnight. Slice chilled and warm slightly before serving.