Cream butter in a large mixing bowl; gradually add sugar, beating well at medium speed of an electric mixer. Add eggs, one at a time, beating well after each addition.
Combine buttermilk and soda, stirring well. Add to creamed mixture alternately with flour, beginning and ending with flour. Add 2 bars (8 oz total) melted chocolate, chocolate syrup, and vanilla. Mix well. Stir in 1 cup chocolate chips.
Pour batter into a heavily greased and floured 10-inch Bundt pan. Bake at 300° for 1 hour and 20 minutes or until a wooden pick inserted in center comes out clean. Invert cake immediately onto a serving plate, and let cool completely.
Combine 4 ounces white chocolate and 2 tablespoons shortening in top of a double boiler; bring water to a boil. Reduce heat to low; cook until melted and smooth. Remove from heat. Drizzle mixture over cooled cake.
Melt remaining 1/2 cup chocolate chips and 2 teaspoons shortening in a small saucepan over low heat, stirring until smooth. Remove from heat, and let cool; drizzle over white chocolate. Garnish with chocolate and white chocolate leaves, if desired.