Special equipment: 8 water balloons
Preheat the oven to 320 degrees F (fan assisted). Grease and flour an 8-inch round cake pan.
For the sponge: In a small bowl, sift together the flour, cocoa powder and baking powder. In a separate, large bowl or stand mixer, whisk together the sugar and eggs until pale and fluffy, 7 to 8 minutes. Add the melted butter and fold it into the eggs, then fold in the dry ingredients.
Pour the batter into the prepared cake pan. Bake until a knife inserted into the center of the cake comes out clean, 30 to 35 minutes. Let cool for 5 minutes, then remove the cake from the pan and set on a rack to cool completely.
For the chocolate bowls: Inflate the water balloons to roughly 4 inches in diameter and tie them off. Place the chocolate and vegetable oil in a heatproof bowl. Set the bowl over a small pan of simmering water and let the chocolate melt, stirring occasional. When fully melted, set the bowl aside for 10 to 15 minutes. (The chocolate will thicken as it stands; you're looking for the thickness of heavy cream.) Dip the balloons in the chocolate and set them on plates covered in lightly oiled plastic wrap. Place in the fridge to set.
When the chocolate has set, coat the balloons with a second layer of chocolate. (You will probably need to reheat the chocolate in the double boiler). Place the balloons back in fridge to set. When fully set, snip off the knots to let the air out; then gently pull the balloons away from the chocolate to reveal the bowls. Refrigerate until ready to serve.
For the cherries: Combine the sugar and 1/2 cup water in a medium saucepan. Bring to a simmer over medium heat. Add the pitted cherries and cook gently for 10 minutes. Remove from the heat and let cool to room temperature. Place in the fridge to chill.
When ready to assemble, cut the cake into small chunks and divide among the chocolate bowls. Top with the cherries and drizzle over some of their syrup.
Whisk the cream and confectioners' sugar to soft peaks. Transfer to a pastry bag fitted with a star tip. Pipe a swirl of cream on top of each bowl. Garnish with one of the reserved cherries. Serve.