Preheat oven to 300°. Grease and flour a 10-cup fluted tube pan.
In a large bowl, beat butter and sugar at medium speed with an electric mixer until fluffy. Add eggs, one at a time, beating well after each addition.
In a medium bowl, combine flour, baking soda, baking powder, and salt. Add to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating after each addition, just until combined. Stir in melted chocolate. Spoon batter into prepared pan.
Bake for 1 hour 30 minutes, or until a wooden pick inserted in center comes out clean. Let cool in pan for 10 minutes. Remove from pan and let cool completely on a wire rack.