The recipe below is for 2 10-inch layers filled and coated in chocolate ganache. My adaptations were to split the layers to create a four-layer cake and use raspberry filling instead of chocolate. To do the same, use half the frosting and all of the raspberry filling, recipe at the end.
For cake layers
3 ounces (85 grams) semi-sweet chocolate
1 1/2 cups (355 ml) hot brewed coffee
3 cups (600 grams) sugar
2 1/2 cups (315 grams) all-purpose flour
1 1/2 cups (aprox. 130 grams; weights vary between brands) unsweetened cocoa powder (not Dutch process)
2 teaspoons (10 grams) baking soda
3/4 teaspoon (4 grams) baking powder
1 1/4 teaspoons (7 grams) table salt
3 large eggs
3/4 cup (175 ml) vegetable oil
1 1/2 cups (355 ml) well-shaken buttermilk
3/4 teaspoon vanilla
For ganache frosting and filling (If you want to just use it for frosting, halve the recipe. A raspberry filling recipe is below.)
1 pound (455 grams) fine-quality semisweet chocolate such as Callebaut
1 cup (235 ml) heavy cream
2 tablespoons (25 grams) sugar
2 tablespoons (40 grams) light corn syrup
1/2 stick (1/4 cup or 55 grams) unsalted butter
Special equipment: two 10- by 2-inch round cake pans
Make cake layers: Preheat oven to 300°F. and grease pans. Line bottoms with rounds of wax paper and grease paper.
Finely chop chocolate and in a bowl 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 layers completely in pans on racks. Run a thin knife around edges of pans and invert layers onto racks. Carefully remove wax paper and cool layers completely. Cake layers may be made 1 day ahead and kept, wrapped well in plastic wrap, at room temperature.
Make frosting: Finely chop chocolate. In a 1 1/2- to 2-quart 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 frosting, whisking until smooth.
Transfer frosting to a bowl and cool, stirring occasionally, until spreadable (depending on chocolate used, it may be necessary to chill frosting to spreadable consistency). I found that stirring this over a bowl of ice water did a great job of cooling it off quickly and evenly.
Spread frosting between cake layers and over top and sides. Cake keeps, covered and chilled, 3 days. Bring cake to room temperature before serving.
2 10-ounce bag frozen raspberries, thawed
1/2 cup sugar
2 tablespoons cornstarch
Puree the raspberries in a food processor, blender or immersion blender. Press the puree through a fine-mesh strainer with the back of a spoon, removing the seeds. Heat the puree in a small pot with the sugar and cornstarch until mixture boils, stirring constantly. As it boils, it should quickly thicken.
Let it cool complete before spreading it thinly over three layers.