Step 1: Prepare the cherry compote

1. In a small saucepan, combine the cherries and sugar. Cook over medium heat until the cherries release their juices and soften, about 5 minutes.
2. Add the cornstarch slurry and cook for another 2-3 minutes, stirring until thickened. Remove from heat and stir in vanilla extract. Let cool completely.

Step 2: Make the chocolate sponge

1. Preheat your oven to 375°F (190°C). Line a 10×15-inch jelly roll pan with parchment paper.
2. In a large bowl, beat the eggs and sugar with a hand or stand mixer on high speed until pale, thick, and tripled in volume (about 5 minutes).
3. Sift together the cocoa powder, flour, baking powder, and salt. Gently fold the dry ingredients into the egg mixture in batches, being careful not to deflate the batter.
4. Spread the batter evenly into the prepared pan. Bake for 8-10 minutes, or until the cake springs back when lightly touched.
5. While the cake is still warm, dust a clean kitchen towel with powdered sugar. Carefully invert the cake onto the towel, peel off the parchment paper, and roll the cake tightly with the towel. Let cool completely.

Step 3: Make the whipped cream

1. In a chilled bowl, whip the heavy cream, powdered sugar, and vanilla extract until stiff peaks form. Refrigerate until ready to use.

Step 4: Assemble the roll

1. Unroll the cooled cake gently. Spread an even layer of whipped cream over the cake, leaving a 1-inch border around the edges.
2. Spoon the cherry compote over the whipped cream.
3. Carefully roll the cake back up, using the towel to guide it, and place seam-side down on a serving plate.

Step 5: Decorate and serve

1. Dust the top with powdered sugar, add chocolate shavings, and garnish with fresh cherries if desired. Refrigerate for 1-2 hours to set before slicing and serving.