Some historians trace this famous cherry-chocolate cake (called Schwarzwälder Kirschtorte in German) back to the 16th century, but it was most likely named and popularized by German baker Josef Keller in 1915 Germans take their world-famous dessert seriously: The cake was granted protected status by the European Commission in 2013, meaning that for a dessert to be sold as a Black Forest Cake, it must contain Black Forest kirsch, a brandy made from local cherries.
Make the cake: Preheat the oven to 350 degrees F. Butter the bottoms and sides of two 9-inch round cake pans; line the bottoms with parchment paper. Butter the parchment and dust the bottoms and sides of the pans with cocoa powder, tapping out the excess.
Put the eggs (in their shells) in a medium bowl and cover with hot tap water; let stand 5 minutes (warming the eggs will help them whip better). Sift the cocoa powder, cake flour and salt into a medium bowl, then whisk in the almond flour; set aside.
Remove the eggs from the water and crack into a large bowl. Add the granulated sugar and beat with a mixer on low speed to combine. Increase the speed to medium high and beat until pale, fluffy and thick, about 10 minutes. The mixture should fall off the beaters in a ribbon when lifted.
Sprinkle one-third of the flour mixture over the egg mixture and gently fold with a whisk until combined. Repeat with the remaining flour mixture in two batches, adding the vanilla with the final addition. Divide the batter evenly between the prepared pans. Bake until the cakes pull away from the sides of the pans and a toothpick inserted into the centers comes out clean, about 25 minutes. Immediately run a small offset spatula around the edges to loosen. Let the cakes cool 5 minutes in the pans, then remove to a rack, parchment-side down, and let cool completely.
Meanwhile, make the whipped cream: Whisk the confectioners' sugar and cornstarch in a small saucepan (the cornstarch will help stabilize the whipped cream). Slowly add 3/4 cup heavy cream, whisking, until a paste forms. Bring to a boil over high heat, stirring, until thick and bubbling, about 1 minute. Transfer to a bowl, place a piece of plastic wrap directly onto the surface and refrigerate until completely cooled, about 30 minutes.
Meanwhile, make the filling: Bring the cherries, cherry syrup, kirsch and granulated sugar to a simmer in a small saucepan, stirring, until the sugar dissolves, 1 to 2 minutes. Stir in the almond extract and transfer to a bowl. Refrigerate 30 minutes.
Finish the whipped cream: Beat the remaining 2 1/4 cups cold heavy cream and vanilla in a large bowl with a mixer on medium-high speed until soft peaks form, about 1 minute. With the mixer running, add the cooked cream mixture and beat until stiff peaks form, 1 to 2 minutes.
Drain the cherries and reserve the syrup. Discard the parchment from the cakes. Trim a thin layer off the top of each cake with a long serrated knife. Put one cake cut-side up on a cake stand or serving plate and brush with half of the reserved syrup. Spread about 1 cup whipped cream over the top in a thin layer, then top with all but 1/4 cup cherries. Spread 1 cup whipped cream over the cherries in a thin layer. Top with the remaining cake and brush with the remaining syrup. Spread 1 1/2 cups whipped cream over the top and sides of the cake in a thin layer (some crumbs are OK). Refrigerate 30 minutes.
Spread the remaining whipped cream over the top and sides of the cake. Refrigerate 30 minutes. Sprinkle the shaved chocolate around the top of the cake and press into the sides; top with the reserved cherries. Refrigerate overnight; the cake will soak up the syrup.