Preheat the oven to 350°F (175°C) and line muffin pans with cupcake liners. In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt. In a separate bowl, combine the sour cream, buttermilk, eggs, vegetable oil, and vanilla extract until smooth.

Gradually add the wet ingredients to the dry ingredients, mixing until just combined. Carefully pour in the hot coffee and stir until the batter is smooth and thin. Avoid overmixing to keep the cupcakes tender.

Divide the batter evenly among the cupcake liners, filling each about two-thirds full. Bake for 18–22 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Let the cupcakes cool in the pans for about 5 minutes before transferring them to a wire rack. Allow them to cool completely before adding the frosting to prevent it from melting.

To make the buttercream, beat the room-temperature butter until creamy. Gradually add the confectioners’ sugar, followed by the vanilla extract and heavy whipping cream. Beat until the frosting is light, fluffy, and easy to pipe.

Divide the buttercream into separate bowls and tint with green, orange, and black gel food coloring. Transfer the colored frosting to piping bags and decorate the cooled cupcakes with Halloween-inspired swirls and designs.

Use the brown M&M’s to create playful faces, eyes, or other spooky details. Pipe the melted chocolate over the cupcakes to make spiderwebs, mouths, or decorative patterns. Allow the chocolate to set before serving, and store the cupcakes in an airtight container until ready to enjoy.