Step 1: Preheat the oven to 350°F (175°C) and line a cupcake pan with paper liners.
Step 2: In a large bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.
Step 3: In a separate medium bowl, combine the eggs, vegetable oil, buttermilk, and vanilla extract.
Step 4: Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Be careful not to overmix.
Step 5: Fill the prepared cupcake liners about two-thirds full with batter and bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let cool completely on a wire rack.
Step 6: While cupcakes cool, gently heat the raspberry or strawberry jam in a small saucepan over low heat until it becomes liquid and easy to spoon. Set aside to cool.
Step 7: Once the cupcakes are cool, use a small knife, a cupcake corer, or the back of a piping tip to remove the center of each cupcake, creating a well.
Step 8: Spoon the cooled jam generously into each cupcake well.
Step 9: Prepare the frosting: In a large bowl, beat the softened unsalted butter until creamy. Gradually add the powdered sugar, heavy cream, vanilla extract, and red food coloring. Beat until the frosting is light, fluffy, and vibrant red.
Step 10: Pipe or spread the frosting on top of each cupcake.
Step 11: Garnish with fresh raspberries on top for an extra 'bloody' decoration, if desired.