Grease and flour a 13- by 9-inch baking pan and set it aside.
Put the oats in a mixing bowl, pour the boiling water over them, and set aside for 20 minutes. Heat the oven to 350ºF.
Combine the shortening, sugars, and eggs in a large mixing bowl. Beat well with an electric mixer, adding the soaked oatmeal.
In a separate bowl, sift together the flour, baking soda, salt, cinnamon, and nutmeg. Beat them into the wet mixture until the batter is evenly mixed.
Pour the batter into the prepared pan. Bake for 30 minutes or until the cake pulls away from the sides or a toothpick inserted into the center comes out clean.
Meanwhile, make the icing. Melt the butter in a medium-size saucepan and stir in the milk.
Add the brown sugar. Bring the mixture to a gentle boil and cook for several minutes, until it reaches the soft ball stage (approximately 235ºF, or when a drop of the icing forms a small ball when dropped into a glass of chilled water).
Remove the pan from the heat and stir in the nuts.
When you take the cake out of the oven, turn on the broiler. Spoon the icing onto the cake and spread it evenly over the top.
Place the cake under the broiler very briefly, just until the icing bubbles over the entire surface it will take only moments. Transfer the cake to a rack and cool, at least slightly, before slicing. Serves 12.