Preheat oven to 350°F (175°C). Grease two 8-inch round cake pans, dust with cocoa powder, and line with parchment paper.
In a stand mixer bowl, combine flour, sugar, cocoa powder, baking soda, baking powder, and salt.
In a separate bowl, whisk oil, buttermilk, eggs, and vanilla. Gradually add hot water or coffee while whisking.
Pour wet ingredients into dry and mix on medium speed for 2–3 minutes until smooth and thin.
Divide batter evenly between pans and bake for 45 minutes or until a tester comes out with moist crumbs.
Cool in pans for 10 minutes, then transfer to a wire rack to cool completely.
For the syrup, heat sugar and cherry juice in a saucepan until dissolved. Simmer 1 minute, optionally add reserved syrup, then cool completely.
Whip cold cream and powdered sugar to stiff peaks. Refrigerate until ready to use.
Melt dark chocolate, spread thinly on parchment, roll into a log, chill until firm, then unroll to create bark pieces.
Slice cooled cakes horizontally into four layers.
Layer cake with cherry syrup, whipped cream, and cherries. Repeat for all layers.
Frost top and sides with remaining cream. Decorate with chocolate bark, shavings, and fresh cherries.
Refrigerate at least 1 hour before slicing and serving.