Make the cake layers: Preheat oven to 325 degrees. Butter two 9-inch round cake pans. Line bottoms with parchment paper; butter parchment. Dust with flour, and tap out excess; set aside. Melt chocolate in a heatproof bowl set over a pan of simmering water, stirring. Let cool completely. Whisk flour, baking powder, and salt in a medium bowl; set aside.
Put butter and sugar into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed until pale and fluffy, 3 to 5 minutes. Reduce speed to low. Mix in buttermilk and vanilla. Add flour mixture in 3 batches, alternating with the eggs, 2 at a time. Add melted chocolate; mix until smooth.
Divide batter between prepared pans. Bake until a cake tester comes out clean, about 30 minutes. Let cool on wire racks 15 minutes. Turn out cakes, and remove parchment. Let cool completely on racks. Cakes can be refrigerated, wrapped tightly in plastic, up to 2 days.
Meanwhile, make the ganache filling: Bring cream to a boil in a medium saucepan over medium-high heat. Pour over chocolate in a heatproof mixer bowl; stir until smooth. Let cool completely. Attach bowl to mixer fitted with the whisk attachment. Beat on medium-high speed until mixture reaches a medium stiff consistency, 2 to 5 minutes, checking frequently. If it does not reach this consistency, chill in freezer up to 5 minutes, then continue beating.
Assemble cake: Trim rounded tops of cakes flat. Stir together 1 1/2 cups filling and the almonds; spread over one cake layer. Top with second layer, and spread remaining filling over top and sides. Smooth with an offset spatula. Refrigerate until filling is very firm, 1 to 2 hours.
Meanwhile, make the ganache glaze: Bring cream to a boil over medium-high heat. Pour over chocolate in a bowl; stir until smooth. Let cool completely.
Transfer assembled cake to a wire rack set over a rimmed baking sheet. Pour glaze over cake all at once, using a spatula to push it over edges and down sides. (This must be done in one pour or the coating will have drips.) Refrigerate until set, 45 minutes to 1 hour.
Make the topping: Put egg whites and sugar into a heatproof mixer bowl set over a pan of simmering water. Whisk until sugar has dissolved and mixture reaches 160 degrees, 4 to 5 minutes. Attach bowl to mixer fitted with whisk attachment. Beat on high speed until stiff peaks form, 7 to 10 minutes. Mound meringue on top of cake; swirl decoratively. Serve.