01 - Preheat oven to 350°F. Grease and flour two 8-inch round cake pans, lining bottoms with parchment paper.
02 - Sift together flour, black cocoa powder, sugar, baking powder, baking soda, and salt in a large mixing bowl.
03 - Whisk oil, milk, eggs, and vanilla extract. Pour into dry ingredients and mix until just incorporated.
04 - Stir in hot water until batter is smooth. Divide evenly between prepared pans. Bake for 35-40 minutes until toothpick inserted in center comes out clean.
05 - Combine cherries, sugar, and lemon juice in saucepan over medium heat. Simmer 5-7 minutes until cherries release juices. Whisk cornstarch with water, stir into cherries, and cook 2-3 minutes until thickened. Cool completely.
06 - Heat heavy cream until just simmering. Pour over chopped dark chocolate and black cocoa powder in heat-proof bowl. Let stand 3 minutes, then whisk until smooth and glossy. Stir in black food coloring if deeper color desired.
07 - Once cakes are completely cooled, trim domed tops if needed. Carefully cut a 4-inch circle about 1-inch deep in center of one cake layer, removing cake plug to create cavity.
08 - Fill cavity with cooled cherry compote. Place second cake layer on top, aligning edges evenly.
09 - Pour black cocoa ganache over top of assembled cake, allowing it to drip down sides. Use offset spatula to spread evenly over entire cake surface. Refrigerate 30 minutes until set.
10 - Pipe red food coloring gel in vein-like patterns on cake surface. Create spider shapes from fondant or melted chocolate and arrange on top. Add edible glitter or sprinkles if desired.