Step #1 To make the frosting: In a large-ish mixing bowl, cream butter & cream cheese; slowly add powdered sugar, beating (with an electric mixer) until mixture is light & fluffy.
Step #2 Stir in vanilla; set aside.
Step #3 To make cake: In a large mixing bowl, cream butter & shortening; slowly add sugar, beating well with an electric mixer at medium speed.
Step #4 Add egg yolks, one at a time, beating well after each addition.
Step #5 In another bowl, mix buttermilk & soda; stir until soda is dissolved.
Step #6 Add flour to creamed mixture alternately with buttermilk mixture, beginning & ending with flour.
Step #7 Mix after each addition.
Step #8 Stir in vanilla.
Step #9 Add in 1 c walnuts & coconut; stir well.
Step #10 In another bowl, beat egg whites (at about room temp) & cream of tartar until stiff peaks form; fold egg white mixture into batter.
Step #11 Pour batter into 3 greased/floured 9-inch round cake pans.
Step #12 Bake in a 350° oven for 22-25 mins or until pick comes out clean.
Step #13 Cool cakes in pans 10 mins; remove this from pans & let cool completely on wire racks.
Step #14 Spread Cream Cheese Frosting between layers & on top & sides of cake.
Step #15 Press extra sliced walnuts onto sides of cake.