01 - Preheat oven to 350°F. Grease and flour two 8-inch round cake pans, then line bottoms with parchment paper.
02 - Sift together flour, black cocoa powder, sugar, baking powder, baking soda, and salt in a large mixing bowl. Whisk until thoroughly combined.
03 - Add vegetable oil, milk, eggs, and vanilla extract to the dry mixture. Beat on medium speed until smooth, approximately 2 minutes.
04 - Slowly stir in hot water until batter is thin and smooth. Divide batter evenly between prepared pans.
05 - Bake for 35 to 40 minutes until a wooden toothpick inserted into the center comes out clean. Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
06 - Combine cherries, sugar, and lemon juice in a medium saucepan over medium heat. Simmer for 5 to 7 minutes until cherries release their juices.
07 - Whisk cornstarch with water until smooth, then stir into cherry mixture. Cook for 2 to 3 minutes until thickened. Transfer to a bowl and refrigerate until completely cold.
08 - Heat heavy cream in a small saucepan until just beginning to simmer. Pour over chopped dark chocolate and black cocoa powder in a heat-proof bowl. Let stand for 3 minutes.
09 - Whisk ganache until smooth and glossy. Stir in black food coloring gel as desired. Let cool at room temperature until spreadable consistency.
10 - Place one cooled cake layer on a serving plate. Using a sharp knife, carefully carve a shallow 4-inch diameter circle in the center, about 1 inch deep, creating a well.
11 - Spoon chilled cherry compote into the cavity. Place second cake layer on top, pressing gently.
12 - Spread black cocoa ganache evenly over the entire cake using an offset spatula. Chill for 30 minutes until ganache is set.
13 - Use red food coloring gel to draw vein-like patterns on the cake surface. Shape fondant or melted chocolate into spider forms and position as desired.