1. 1Heat the oven to 350°F and arrange a rack in the middle. Cut out 2 (8-inch) rounds of parchment paper. Coat 2 (8-inch) cake pans with butter, place the rounds in the pans, and coat the parchment with more butter. Coat the pans and parchment with flour and tap out any excess; set aside.
2. 2Bring the water to a boil over high heat in a medium saucepan. Remove from the heat, add the chocolate and cocoa, and whisk until smooth; set aside to cool for 10 minutes.
3. 3Whisk together the measured flour, baking soda, and salt in a medium bowl until combined; set aside.
4. 4Place the measured butter and sugar in the bowl of a stand mixer fitted with a paddle attachment and beat on medium speed until fluffy and light in color, about 5 minutes. Stop the mixer and scrape down the sides of the bowl and the paddle with a rubber spatula.
5. 5Return the mixer to medium speed. Add the eggs 1 at a time, letting each incorporate fully before adding the next. Add the sour cream and vanilla and beat until just combined (the mixture will look slightly curdled). Stop the mixer and scrape down the sides of the bowl and the paddle.
6. 6Add a third of the reserved flour mixture and turn the mixer to low speed, mixing until the flour is just incorporated. Add half of the cooled chocolate mixture and mix until just incorporated. Continue with the remaining flour mixture and chocolate mixture, alternating between each and ending with the flour, until all of the ingredients are incorporated and the mixture is smooth. Stop the mixer, remove the bowl, and stir in any remaining flour streaks by hand, making sure to scrape the bottom of the bowl.
7. 7Divide the batter evenly between the prepared pans and spread it into even layers. Bake them side by side on the rack for 15 minutes. Rotate the pans from left to right and continue baking until the cake edges slightly pull away from the pans and a cake tester or toothpick inserted into the center comes out dry with just a few crumbs, about 14 to 15 minutes more.
8. 8Remove the pans from the oven and let them cool on a wire rack for 45 minutes. Run a knife around the perimeter of each cake, turn them out onto the rack, and slowly peel off and discard the parchment rounds. Flip the cakes over and let them cool completely. Meanwhile, make the syrup.

For the cherries and syrup:

1. 1Place a fine-mesh strainer over a small saucepan and pour the cherries and their syrup through the strainer. Cut the cherries in half and place them in a medium bowl.
2. 2Bring the syrup to a boil over medium-high heat. Reduce the heat to medium low and simmer until reduced to 1/3 cup, about 10 to 12 minutes. Remove from the heat and stir in the kirsch and lemon juice.
3. 3Add 2 tablespoons of the syrup to the reserved cherries and stir to combine; set aside. Set aside the remaining syrup until ready to assemble the cake, letting it cool completely, about 30 minutes. Meanwhile, make the whipped cream filling.

For the whipped cream filling:

1. 1Place the sugar and cornstarch in a small saucepan. While stirring constantly, pour in 1/4 cup of the cream. Place the pan over medium heat and, stirring constantly, bring to a boil (it will be lumpy, but will smooth out). Remove from the heat, stir in the vanilla, and let cool completely, about 30 minutes. Meanwhile, place the remaining 3/4 cup cream in the bowl of a stand mixer and refrigerate.
2. 2When the cornstarch-cream mixture has cooled, fit the chilled bowl of cream onto the stand mixer. Using the whisk attachment, whisk on medium speed until tracks begin to show in the cream, about 40 to 60 seconds. With the mixer still on, slowly add the cornstarch mixture and continue whisking until stiff peaks form, about 30 to 60 seconds more. Refrigerate until ready to assemble the cake.

To assemble:

1. 1When the cakes are cool, use a serrated knife to trim a thin layer from the top of each to expose the interior; discard the scraps and set the cakes aside. Using a skewer, poke holes all over the tops of the cakes, going about halfway through the layers. 
2. 2Place 1 cake layer cut-side up on a cake stand or serving plate. Use a pastry brush to brush half of the reserved syrup over the cake. Spread half of the whipped cream evenly over top of that, leaving a 3/4-inch border. Using a slotted spoon, evenly scatter the reserved cherries over the cream, leaving any syrup in the bowl. Dollop the remaining whipped cream over the cherries and spread it into an even layer, leaving a 3/4-inch border. 
3. 3Place the second cake round cut-side up on top of the whipped cream and press down gently. Brush the cake with the remaining half of the syrup. 
4. 4Using all of the frosting, evenly coat the top and sides of the cake. To create the tree-stump effect, use the tip of an offset spatula to make shallow vertical lines in the side of the cake, spacing the lines about 1/2 inch apart and wiping the spatula clean on a moist paper towel every few swipes. Then use a table knife to make deeper, thinner vertical lines in the shallow swipes, spacing them about 1 inch apart. Using the tines of a fork, draw concentric circles in the frosting on top of the cake. 

5. 

   For the cake:

   • 1 1/4 cups water
   • 4 ounces unsweetened chocolate, finely chopped
   • 1/2 cup Dutch-process cocoa powder
   • 1 3/4 cups all-purpose flour, plus more as needed
   • 1 1/2 teaspoons baking soda
   • 1/2 teaspoon fine salt
   • 12 tablespoons unsalted butter (1 1/2 sticks), at room temperature, plus more as needed
   • 1 3/4 cups granulated sugar
   • 3 large eggs, at room temperature
   • 1/2 cup sour cream, at room temperature
   • 1 1/2 teaspoons vanilla extract

   For the cherries and syrup:

   • 1 (15-ounce) can dark sweet cherries in heavy syrup
   • 2 tablespoons kirsch or cherry-flavored liqueur
   • 1 tablespoon freshly squeezed lemon juice

   For the whipped cream filling:

   • 2 tablespoons granulated sugar
   • 1 teaspoon cornstarch
   • 1 cup cold heavy cream
   • 1/2 teaspoon vanilla extract

   To assemble:

   • 2 recipes Bittersweet Chocolate Frosting
   • 10 (2- to 3-inch) fresh rosemary branches
   • 1 large egg white, at room temperature
   • Powdered sugar, for dusting
   • 10 fresh cranberries
   • Meringue Mushrooms