Dissolve soda in buttermilk; stir well, and set aside.
Cream butter; gradually add sugar, beating until light and fluffy. Add eggs, one at a time, beating well after each addition. Set aside.
Combine flour and pumpkin pie spice; add to creamed mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Fold jam into batter.
Pour batter into 3 waxed paper - lined and heavily greased 9 - inch round cake pans. Bake at 350° for 4 0 to 5 0 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove layers from pans, and let cake cool completely.
Spread Egg Nog Icing between layers and on top and sides of the cooled cake.