Preheat oven to 350°F (175°C). Line a 15×10-inch jelly roll pan with parchment paper.
In a large bowl, beat eggs and granulated sugar until thick and pale.
Sift together flour, cocoa powder, baking powder, and salt. Gently fold into the egg mixture.
Pour batter into prepared pan and spread evenly.
Bake for 12-15 minutes until the cake springs back when touched.
Immediately invert the cake onto a clean kitchen towel dusted with powdered sugar. Peel off parchment paper.
Roll the cake with the towel from the short side. Let cool completely rolled.
Whip heavy cream with powdered sugar and vanilla extract until stiff peaks form.
Mix pitted sour cherries with Kirsch.
Unroll the cooled cake and spread whipped cream evenly over it.
Scatter cherry mixture over the cream, then gently re-roll the cake without the towel.
Place the roll on a serving plate diagonally.
Top with whipped cream rosettes, cherries, and dark chocolate shavings.
Drizzle a small amount of cherry syrup beside the roll for garnish.