Cream butter and sugar until light and fluffy, about 5 minutes.
Add eggs one at a time beating after each addition.
Add cocoa, oil, & melted chocolate. Stir gently.
Add vanilla and milk stirring gently, but well.
Stir in flour, baking powder, & soda just until mixed.
Pour batter into greased bundt pan or 9 by 13 pan.
Bake for 25 minutes for 9 by 13 and then check, 35 minutes for bundt pan and then check. You will probably end up at 35 for a 9 by 13 and 45 for the bundt pan.
If using the bundt pan, let cool for about 5 minutes before turning out on to a cooling rack and allow to cool completely before adding the chocolate frosting.