Step 1: Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. Line the bottoms with parchment paper.
Step 2: In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.
Step 3: In a separate medium bowl, whisk together buttermilk, oil, eggs, and vanilla extract.
Step 4: Pour the wet ingredients into the dry ingredients and mix on low speed until just combined. Slowly add the hot coffee (or water) and mix until the batter is smooth. Do not overmix.
Step 5: Divide batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Step 6: Let cakes cool in pans for 10-15 minutes, then invert onto a wire rack to cool completely.
Step 7: For the cherry filling, combine cherries, sugar, cornstarch, and water in a medium saucepan. Cook over medium heat, stirring constantly, until thickened and bubbly, about 5-7 minutes. Remove from heat, stir in lemon juice and almond extract (if using). Let cool completely.
Step 8: For the frosting, in a large bowl, beat softened butter and cream cheese with an electric mixer until light and fluffy.
Step 9: Gradually add sifted powdered sugar and cocoa powder, beating until smooth. Add vanilla extract and salt. If frosting is too thick, add heavy cream 1 tablespoon at a time until desired consistency is reached.
Step 10: To assemble, place one cooled cake layer on a serving plate. Spread about 1/3 of the frosting evenly over the top. Create a border with frosting and spoon half of the cherry filling inside the border.
Step 11: Place the second cake layer on top. Repeat with another 1/3 of the frosting and the remaining cherry filling.
Step 12: Top with the third cake layer (if using 3 layers, adjust frosting distribution). Frost the top and sides of the entire cake with the remaining frosting.
Step 13: Garnish with fresh cherries and chocolate shavings, if desired. Chill the cake for at least 30 minutes before slicing for easier serving.