Preheat oven to 350°F (175°C). Line a muffin tin with cupcake liners.

Prepare chocolate cake batter according to package directions. Divide batter into liners and bake 18–20 minutes, or until a toothpick comes out clean. Cool completely.

In a small bowl, mix jam with red food coloring if desired for a more dramatic 'blood' filling.

Once cupcakes are cool, use a piping tip or small knife to cut a hole in the center of each cupcake. Fill with jam mixture, then replace the top piece of cake.

In a large bowl, beat butter until creamy. Gradually mix in powdered sugar, vanilla, salt, and 2–3 tablespoons of milk until frosting is smooth and spreadable.

Frost cupcakes with buttercream.

To decorate, poke two small holes in the frosting using a skewer or straw to mimic vampire fangs. Drizzle red gel icing or extra jam from the holes to resemble dripping blood.