Heat oven to 300° F. Grease and flour pans; line bottoms with parchment paper; grease tops of parchment paper.

Prepare hot coffee and pour into heat-resistant bowl. Add chocolate and let mixture stand for a couple minutes. Stir until chocolate is melted and mixture is smooth.

In large mixing bowl sift together sugar, flour, cocoa powder, baking soda, baking powder, and salt.

In bowl of stand 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 well-combined.

Slowly add flour mixture and beat on medium until well-combined.

Divide batter between pans and bake in middle of oven until a tester inserted in center comes out clean.

Cool layers completely in pans on racks. Run a knife around edges of pans and invert layers onto racks. Cake layers can be made a day ahead and stored at room temperature.

Finely chop chocolate. In a 1 1/2- to 2-quart saucepan, add cream, sugar, and corn syrup.

On medium low heat, bring to a boil, whisking until sugar is dissolved.

Remove pan from heat and add chocolate, whisking until chocolate is melted. Add butter pieces to frosting, whisking until smooth.

Let frosting cool, stirring occasionally, until spreadable (depending on chocolate used, it may be necessary to chill frosting to spreadable consistency). Spread frosting between cake layers and over top and sides. Cake keeps, covered and chilled, 3 days. Bring cake to room temperature before serving.