01 - Preheat oven to 350°F. Grease two 8-inch round cake pans with butter and line bottoms with parchment paper.
02 - Sift flour, black cocoa powder, sugar, baking powder, baking soda, and salt into a large mixing bowl. Whisk until fully combined.
03 - Create a well in center of dry ingredients. Pour in vegetable oil, milk, eggs, and vanilla extract. Beat with electric mixer on medium speed until smooth.
04 - Slowly stir hot water into batter, mixing until completely incorporated. Batter will appear thin.
05 - Divide batter evenly between prepared pans. Bake 35 to 40 minutes until wooden pick inserted in center comes out clean. Cool in pans 10 minutes, then transfer to wire rack to cool completely.
06 - Combine cherries, sugar, and lemon juice in medium saucepan. Cook over medium heat 5 to 7 minutes until cherries release juices. Whisk cornstarch into water, add to cherries, and cook 2 additional minutes until thickened. Transfer to bowl and cool completely.
07 - Heat heavy cream in small saucepan until just simmering. Place chopped chocolate and black cocoa powder in heat-proof bowl. Pour hot cream over chocolate. Let stand 3 minutes, then whisk until completely smooth. Add black food coloring gel to deepen color if desired. Cool until thickened but spreadable.
08 - Place one completely cooled cake layer on serving plate. Using small knife, carefully cut shallow circle in center of cake, leaving 1-inch border on all sides. Remove cake center, creating cavity for filling.
09 - Spoon cooled cherry compote into cavity. Place second cake layer on top, pressing gently to secure.
10 - Spread black cocoa ganache evenly over top and sides of cake using offset spatula. Chill 20 minutes until set.
11 - Create spider web vein patterns on cake surface using red food coloring gel. Form spider shapes from fondant or piped chocolate. Add edible glitter for dramatic effect.