Cream butter in a large mixing bowl; gradually add sugar, beating until light and fluffy. Add egg yolks; beat well.
Dissolve soda in buttermilk; stir well. Combine 2 1/2 cups flour and spices; add to creamed mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Mix well after each addition.
Dredge pecans in remaining 1/2 cup flour; fold pecans and pear preserves into batter. Beat egg whites (at room temperature) until stiff peaks form; gently fold into batter.
Pour batter into 3 waxed paper - lined and heavily greased 9 - inch round cake pans. Bake at 350° for 35 to 40 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 Heritage Caramel Frosting between layers and on top and sides of cooled cake.