Preheat Oven to 300 degrees F. Line two 9 inch round pans with parchment paper and grease the paper and sides of pans.
Finely chop the chocolate. Combine with hot water. Let mixture stand, stirring occasionally, until chocolate is melted and mixture is smooth.
Into a large bowl, sift together sugar, all purpose flour, cocoa powder, baking soda, baking powder and salt.
In another large bowl with an electric mixer, beat the eggs until slightly thickened (about 3 minutes with a standing mixer)
Slowly add oil, buttermilk, vanilla and melted chocolate mixture to the eggs, beating until combined. Add sugar mixture and beat on medium speed until just combined well.
Divide batter between pans and bake in middle of oven until a tester inserted in center comes out clean. About 1 hour to 1 hour and 10 minutes.