Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners. In a large mixing bowl, cream together the softened butter and sugar until light and fluffy, about 2-3 minutes. Add the eggs one at a time, beating well after each addition.

Mix in the vanilla extract and red food coloring. In a separate bowl, whisk together the flour, cocoa powder, and salt. Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk, until just combined.

Stir in the baking soda and vinegar mixture. Spoon the batter into the prepared muffin tin, filling each cup about ⅔ full. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let the cupcakes cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.

Carefully remove the paper liners to expose the deep red sides of the cupcakes.

In a small bowl, combine the red velvet cake crumbs with the sweetened condensed milk and melted butter. Stir until the mixture is smooth and slightly glossy. Add red food coloring to achieve an intense, vibrant red.

Once cooled, use a small knife or cupcake corer to remove a small section from the center of each cupcake. Fill each hole with the creamy red velvet filling.

In a large bowl, beat the softened butter until creamy. Gradually add the powdered sugar, mixing well after each addition. Add the vanilla extract and 2 tablespoons of milk or cream, beat until smooth.

Frost each cupcake with the pale buttercream using an offset spatula or a piping bag. Use candy fangs or drops of red gelatin to create two close-set puncture marks, drizzle red syrup or edible gel from the puncture marks.

Arrange the decorated cupcakes on a dark serving platter, surrounded by additional red syrup drips for an extra spooky effect.