sweet potato bread

my mom used to make this when i was a kid and i LOVED it. i wold do my best to eat the whole loaf myself whenever she made it.

1/2 c butter, softened
1/2 c shortening
2 2/3 c sugar
4 eggs
2 c mashed sweet potatoes
3 1/2 c sifted flour
2 teaspoons salt
1 teaspoon cinnamon
1 1/2 teaspoons nutmeg
2 teaspoons baking soda
1 c chopped walnuts (optional)
2/3 c strong black coffee (the juice from canned sweet potatoes works well as a substitute)

cream butter, shortening, and sugar, add eggs one at a time, then blend in sweet potatoes. sift together dry ingredients and add nuts. stir into potato mixture, alternating w/ coffee. pour into 2 greased loaf pans and bake at 375 for 1 hour (or 25 minutes for muffins). cool 10 minutes before removing from pans.