This recipe is from Betty Crocker's Cook book for Boys and Girls, Susan's first childhood cookbook, which was published in 1957. She said it was such a thrill to "discover" actual recipes. A classic for sure.
Heat oven to 350°F. Grease and flour two 8-inch round cake pans.
In a mixing bowl whisk together cake flour, sugar, baking powder and salt. Add shortening, ⅔ cup milk and vanilla and beat on medium speed until shortening is incorporated, about 2 min. Add remaining ⅓ cup milk and eggs and beat 2 min.
Pour batter into prepared pans and bake until golden brown and a toothpick inserted into center comes out clean, 30 to 35 min. Cool in pans 15 min, then turn out and cool completely.
Make frosting: Combine melted chocolate and butter and stir on medium-low speed until creamy and glossy, about 2 min.
Trim domed tops from cooled cakes. Place one layer on a cake plate and spread with ¾ cup frosting, then top with second layer. Cover entire cake with remaining frosting.