Place a rack in the middle of the oven and preheat the oven to 325°.
Butter 2 loaf pans (9x5x3 x 2 1/4-inch), then line the bottoms with parchment or wax paper.
Sift the cake flour, baking powder, salt, and nutmeg together into a medium-size bowl and set aside.
Cream the butter and shortening in a large bowl with an electric mixer on high until light yellow, about 5 minutes.
Then, while the mixer is still running, add the sugar, about 1/2 cup at a time, beating 1 to 2 minutes after each addition.
Now add the eggs, one at a time, beating 3 minutes after adding each one.
Beat the batter until it is light yellow, airy, and starts crawling up the sides of the bowl, a total of about 35 minutes in all. (this is important)
Beat in the vanilla.
Sift about one fourth of the flour mixture over the batter and stir it in by hand, then stir in one third of the milk.
Repeat by adding one-quarter more flour, one third more milk, another one fourth of the flour, then the rest of the milk.
Finally, stir in the rest of the flour.
Stir after each addition until the ingredients are well incorporated.
Gently spoon half of the batter into each loaf pan.
Set the 2 pans side by side in the oven, making sure they are not touching each other.
Bake the cakes until the tops are golden and the center of each cake springs back when you touch it lightly and a toothpick inserted in the center comes out with moist crumbs (not batter) clinging to it, about 1 hour.
Let the cakes cool on a wire rack for 30 minutes before removing them from the pans.
Note: I am assuming that the 35 minutes total beating time includes all additions to the batter as well.