Cream shortening, butter, and brown sugar. Gradually add eggs.
Sift flour, soda, salt, and spice and alternate with milk.
Add dates and nuts.
Bake in 9-inch layers at 350°F for 30 minutes.
Cool, then frost with Penuche Frosting.
Melt butter in medium saucepan.
Stir in brown sugar and boil for 2 minutes, stirring constantly.
Add milk and heat to boiling.
Remove from heat; cool and beat in powdered sugar.
I believe that the reason for 1/2 butter and 1/2 shortening was economy. All butter would probably work well, too. Margarine contains liquid, so it wouldn't be the best choice.
Be sure to use 9-inch cake pans, or you'll have cake everywhere. Three thinner, 8-inch cakes could probably be made instead, but I've never tried it.