Preheat the oven to 350°F (175°C). Line a 12-cup muffin pan with cupcake liners.

Whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.

Add the egg, milk, vegetable oil, and vanilla extract. Mix until just combined.

Slowly add the hot water and mix until the batter is smooth.

Divide the batter evenly between the cupcake liners, filling each about two-thirds full.

Bake for 17–19 minutes, or until a toothpick inserted in the center comes out clean.

Cool the cupcakes completely before decorating.

Beat half of the butter until creamy. Gradually add 1 cup powdered sugar, 1 tablespoon milk, vanilla, and orange food coloring. Beat until fluffy.

For the chocolate frosting, beat the remaining butter with the remaining powdered sugar, milk, vanilla, and cocoa powder until smooth.

Pipe the orange and chocolate frosting onto the cooled cupcakes.

Add candy eyes, black and orange sprinkles, and mini ghost decorations.

Drizzle or pipe melted chocolate into thin spiderweb designs over the frosting.

Let the decorations set, then serve and enjoy!