Preheat the oven to 350 degrees and line a muffin tin with four paper liners.

In a medium bowl, whisk together the flour, black cocoa powder, baking soda, salt, and granulated sugar.

In a separate bowl, beat the egg, buttermilk, vegetable oil, and vanilla extract until smooth.

Pour the wet mixture into the dry ingredients and stir until just combined, then slowly add the hot coffee and mix until the batter is thin but uniform.

Divide the batter evenly among the four liners and bake for 18 to 20 minutes, or until a toothpick inserted in the center comes out clean. Cool completely on a wire rack.

While the cupcakes cool, beat the softened butter until creamy, then gradually add the powdered sugar and milk until the frosting reaches a spreadable consistency.

Tint a small portion of the frosting with black food coloring and set it aside for piping. Spread the remaining white frosting over each cooled cupcake.

Pipe thin black circles on top of the white frosting, then drag a toothpick from the center outward to create the spiderweb pattern.