01 - Preheat oven to 350°F. Grease and line two 8-inch round cake pans with parchment paper.
02 - In a large bowl, whisk together flour, black cocoa powder, sugar, baking powder, baking soda, and salt until evenly combined.
03 - Add vegetable oil, milk, eggs, and vanilla extract to the dry mixture. Beat until fully incorporated and smooth.
04 - Stir hot water into batter until completely smooth. Divide batter evenly between prepared pans. Bake for 35 to 40 minutes or until a toothpick inserted in center comes out clean. Cool completely in pans before removing.
05 - Combine pitted cherries, sugar, and lemon juice in a saucepan. Simmer over medium heat for 5 to 7 minutes until cherries release juices. Whisk cornstarch with water until smooth, then stir into cherry mixture. Cook until thickened, about 2 minutes. Cool completely.
06 - Heat heavy cream in a small saucepan until just simmering. Pour hot cream over chopped dark chocolate and black cocoa powder in a heat-proof bowl. Let stand for 3 minutes, then whisk until completely smooth and glossy. Add black food coloring gel if deeper color desired.
07 - Place one cooled cake layer on serving plate. Using a small spoon, carefully hollow out a shallow circular cavity in center of cake layer, leaving about 1-inch border on all sides.
08 - Fill hollowed cavity completely with cooled cherry compote. Place second cake layer on top, pressing gently to secure.
09 - Spread black cocoa ganache evenly over top and sides of assembled cake using offset spatula. Chill for 20 to 30 minutes until ganache sets firm.
10 - Create red vein patterns on cake surface using red food coloring gel and fine brush or toothpick. Form spider shapes from fondant or melted chocolate. Arrange spiders decoratively and add edible glitter as desired.