Melt chocolate bars in syrup over hot, not boiling water. Cream butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Blend in vanilla and chocolate mixture. Stir baking soda into buttermilk; add alternately with flour to creamed mixture. Beat two minutes at medium speed. Pour batter into a greased and floured 10 inch tube pan. Bake at 350 for 1 hour and 15 to 20 minutes. Allow cake to cool in pan. Remove from pan and sprinkle with confectioners sugar.