Preheat oven to 300º and grease pans. Line bottoms with rounds of wax paper and grease paper.
Finely chop chocolate and combine in a bowl with hot coffee.
Let mixture stand, stirring occasionally until chocolate is melted.
In another large bowl, sift together sugar, flour, cocoa powder, baking soda, baking powder and salt.
In another bowl, or a stand mixer, beat eggs with an electric mixer until thickened slightly and lemon colored (about 3 minutes with a stand mixer or 5 minutes with a hand-held).
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 the middle of oven until a tester inserted in center comes out clean, about 1 hour to 1 hour 10 minutes. It is easy to overbake. Be careful.
In a sauce pan, combine bring cream, sugar, and corn syrup to a boil over moderately low heat, whisking until sugar is dissolved. Remove pan from heat and add finely chopped chocolate (or chips), whisking until chocolate is melted. Cut butter into pieces and add to frosting, whisking until smooth.
Transfer frosting to a bowl and cool, stirring occasionally, until spreadable (I find you have to put it in the refridgerator for a while),
Cake keeps covered and chilled for 3 days. Bring to room temperature before serving.