Step 1

Preheat oven to 325˚F. Beat butter with an electric mixer on medium speed until creamy, 2 to 3 minutes. Gradually add sugar, beating well. Add eggs, 1 at a time, beating well after each addition.

Step 2

Stir together baking soda and buttermilk in small bowl until baking soda is dissolved. Stir together flour and salt in a large bowl; add to butter mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Beat well on medium speed after each addition. Add melted chocolate, beating well. Beat in vanilla on low speed. Pour batter into a greased (with shortening) and floured 10-inch tube pan.

Step 3

Bake in preheated oven until a wooden pick inserted in center comes out clean, about 1 hour and 25 minutes. Cool in pan 15 minutes; remove cake from pan, and let cool completely, about 1 1/2 hours.  Sprinkle with powdered sugar.