Direction :

1. Preheat oven to 300°F. and grease pans or pan (see note above). Line pan or pans with round of parchment paper. Finely chop chocolate and in a bowl combine with boiling water or hot coffee. Let mixture stand, stirring occasionally, until chocolate is melted and mixture is smooth.
2. Into a large bowl sift together sugar, flour, cocoa powder, baking soda, baking powder, and salt. (If you don’t feel like sifting, whisking is fine, too.)
3. In another large bowl whisk egg vigorously until thickened slightly and lemon colored (about 3 minutes). Slowly add oil, buttermilk, vanilla, and melted chocolate mixture to egg, beating until combined well. Add sugar mixture and whisk until just combined. Divide batter between pans (or pan, see notes above) and bake in middle of oven until a tester inserted in center comes out clean, about 45 minutes for smaller pans, 55 minutes or longer for larger pans. Note: I simply touch with my finger, and if it feels mostly springy, I remove the pans from the oven.
4. Meanwhile, make the ganache: Finely chop chocolate. In a small saucepan bring cream, sugar, and corn syrup to a boil over moderately low heat, whisking until sugar is dissolved. Remove pan from heat and add chocolate, whisking until chocolate is melted. Cut butter into pieces and add to chocolate mixture, whisking until smooth. Season with sea salt to taste, if desired.
5. Cool cake layers completely in pans on racks, at least 30 minutes. Run a thin knife around edges of pans and invert layers onto racks. Remove parchment paper and cool layers completely. Cake layers may be made 1 day ahead and kept, wrapped well in plastic wrap, at room temperature.
6. If you are making a layer cake, spread a thin layer of ganache over one cake layer. (Note: If you baked a single layer, halve it crosswise with a serrated knife, and spread ganache over top of one layer.) Top layer with other cake layer. Pour ganache on top of top layer, and with an off-set spatula, spread it all over the sides. If desired, run square of chocolate across a microplane grater or shave with a peeler until top of cake is covered in chocolate shavings. Cake keeps, covered and chilled, 3 days. Bring cake to room temperature before serving. (I just keep mine at room temperature always…no space in the fridge.)