Preheat oven to 350°F (175°C) and line a muffin tin with cupcake liners.
Prepare cake mix according to package directions and divide batter evenly among liners.
Bake 18–20 minutes, or until a toothpick inserted in the center comes out clean. Cool completely.
Using a small knife or cupcake corer, cut a small hole in the center of each cupcake. Fill with about 1 teaspoon of jam to create the bloody center.
Make the frosting: beat softened butter and cream cheese until smooth. Add powdered sugar gradually, then mix in vanilla and enough cream to reach fluffy, spreadable consistency.
Frost cupcakes with cream cheese frosting, smoothing tops flat.
To make vampire bites: use a toothpick or straw to poke two small holes in the frosting, close together, to resemble fang marks.
Drip a little red gel or jam from each hole so it looks like blood is oozing out.
Optional: drizzle extra jam for a dramatic bloody effect.