Step 1: Preheat your oven to 350°F (175°C). Line a 12-cup cupcake pan with cupcake liners. This ensures that the cupcakes don't stick to the pan and makes for easy removal.
Step 2: In a medium bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking soda, and salt. Whisking ensures that the dry ingredients are evenly distributed, which is crucial for a consistent texture.
Step 3: In a small bowl, mix together the buttermilk, red food coloring, and vanilla extract. The buttermilk adds moisture and tanginess to the cupcakes, while the red food coloring gives them their signature vibrant color. The vanilla extract enhances the overall flavor.
Step 4: In a large bowl, cream together the softened unsalted butter and granulated sugar until light and fluffy. This step is essential for creating a light and airy texture in the cupcakes. Use an electric mixer for best results.
Step 5: Add the large egg to the butter and sugar mixture and mix until fully incorporated. Ensure that the egg is at room temperature for better emulsification.
Step 6: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk mixture, beginning and ending with the dry ingredients. Mix until just combined. Be careful not to overmix the batter, as this can result in tough cupcakes.
Step 7: Gently swirl blackberry jam into the cupcake batter, creating a marble effect. Be careful not to overmix to maintain the distinct swirl pattern.
Step 8: Fill each cupcake liner about ⅔ full. This will prevent the cupcakes from overflowing during baking.
Step 9: Bake in the preheated oven for 17–19 minutes, or until a toothpick inserted into the center comes out clean. The baking time may vary depending on your oven, so it's important to check the cupcakes for doneness.
Step 10: Let the cupcakes cool completely in the pan before frosting. Cooling completely prevents the frosting from melting and ensures that the cupcakes hold their shape.
Step 11: While the cupcakes are cooling, prepare the cream cheese frosting. In a large bowl, beat together the softened cream cheese and unsalted butter until smooth and creamy.
Step 12: Gradually add the powdered sugar to the cream cheese mixture, beating until light and fluffy. The powdered sugar sweetens the frosting and gives it a smooth, creamy texture.
Step 13: Add the vanilla extract to the frosting and mix until well combined.
Step 14: Once the cupcakes are completely cooled, frost them generously with the cream cheese frosting using a piping bag or a knife.
Step 15: Sprinkle the frosted cupcakes with crushed freeze-dried raspberries and garnish with fresh mint leaves, if desired. The crushed raspberries add a burst of flavor and a beautiful pop of color, while the mint leaves provide a refreshing aroma.