Preheat oven to 300 F
Grease pans. Line bottoms with wax paper and grease the paper as well
Chop chocolate and combine with hot coffee. Let mixture stand, stirring occasionally, until chocolate is melted and mixture is smooth.
Into a large bowl sift together sugar, flour, cocoa powder, baking soda, baking powder, and salt.
In another large bowl with an electric mixer beat eggs until thickened slightly and lemon colored (about 3 minutes with a standing mixer or 5 minutes with a hand-held mixer). Slowly add oil, buttermilk, vanilla, and melted chocolate mixture to eggs, beating until combined well.
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, 1 hour to 1 hour and 10 minutes.
Cool cakes completely in pans on racks.