Preparation Steps

• Prepare the white chocolate 'blood' first so it has time to cool: heat the heavy cream, rose water, and a pinch of salt in a small saucepan just until it starts to steam (do not boil).
• Pour the hot cream over the white chocolate in a heatproof bowl, cover and let sit 2–3 minutes. Stir until smooth; once homogeneous, stir in the red gel food coloring and a single tiny drop of brown gel to achieve a realistic blood tone. Set the ganache aside at room temperature, then refrigerate briefly until thick but still pipeable (about 30–40 minutes).
• Preheat oven to 350°F (175°C). Line three 12-cup muffin tins with paper liners (you’ll have extra batter — see note).
• Whisk together flour, black cocoa, baking powder, baking soda, and salt in a large bowl. In a separate bowl, combine sugar and softened butter and beat until light and slightly fluffy (about 2–3 minutes).
• Add eggs one at a time to the butter-sugar mixture, mixing well after each. Stir in vanilla and the dissolved espresso. Alternate adding the dry mix and buttermilk (beginning and ending with dry), mixing on low until just combined. Fold in sour cream, oil, and black gel coloring until the batter is smooth and very dark.
• Spoon batter into liners using a 3 Tbsp scoop (fill about two-thirds full). Bake on the middle rack for 18–22 minutes, rotating pans when you swap racks if baking in batches. Cupcakes are done when a toothpick near the center comes out with a few moist crumbs.
• Cool cupcakes in the pan for 5 minutes, then transfer to a wire rack to cool completely before filling and frosting.
• While cupcakes cool, make the black buttercream: beat softened butter on medium speed until creamy (about 2 minutes). Add powdered sugar and black cocoa in three additions, alternating with heavy cream. Mix in vanilla, salt, and black gel food coloring. Beat on high for 1–2 minutes until light and pipeable; add extra cream 1 Tbsp at a time if too stiff.
• Core each cooled cupcake by cutting a cone-shaped plug from the center (reserve the plug for snacking). Pipe or spoon the chilled white chocolate ganache into the cavity, leaving it level with the top of the cake.
• Fit a piping bag with a large star tip and fill with the black buttercream. Pipe a generous swirl over each filled cupcake. For extra drama, make a shallow well in the center of the swirl and drop a tiny extra dot of red gel (or a drop of the ganache) so when bitten the 'blood' flows out.
• Scatter sprinkles over the swirls while the buttercream is still soft. Chill cupcakes briefly to set the buttercream for traveling, but bring to room temperature before serving for the best texture.
• Serve with a friendly warning that the cupcakes are filled and may 'bleed' when bitten. Store leftover cupcakes in an airtight container in the refrigerator for up to 4 days; bring to room temperature before eating.