01 - Preheat oven to 350°F (175°C). Line a standard 12-cup muffin tin with cupcake liners.
02 - In a medium mixing bowl, whisk together all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, and salt until evenly blended.
03 - In a large bowl, use an electric mixer to beat softened butter and granulated sugar together until the mixture is light and fluffy. Incorporate eggs one at a time, followed by vanilla extract.
04 - Add half of the dry mixture to the wet ingredients and mix until just combined. Add whole milk and mix again. Fold in remaining dry ingredients and stir in hot water until the batter is smooth.
05 - Divide the batter evenly among the cupcake liners, filling each about two-thirds full. Bake for 18 to 20 minutes, or until a toothpick inserted into the center comes out clean.
06 - Allow cupcakes to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely before filling and frosting.
07 - In a small saucepan over medium heat, combine raspberries, granulated sugar, and lemon juice. Stir periodically until the raspberries break down. Add cornstarch mixture and cook for 1–2 minutes until thickened. Remove from heat and cool entirely.
08 - Using a sharp knife or cupcake corer, remove a small section from the center of each cooled cupcake. Fill each cavity with raspberry mixture.
09 - Beat softened butter in a clean bowl until creamy. Gradually add sifted powdered sugar, followed by whole milk, vanilla extract, and a pinch of salt. Continue beating on medium-high speed until light and fluffy.
10 - Apply frosting to the tops of cupcakes using a piping bag or spatula. Drizzle with edible fake blood or extra raspberry filling. For a dramatic effect, embellish with red gel food coloring and white chocolate fangs as desired.