Preheat your oven to 350°F (175°C) and line a cupcake pan with 12 cupcake liners.

In a small bowl, sift together flour, cocoa powder, baking powder, baking soda, salt, and optional espresso powder. Set aside.

In a large mixing bowl, beat the cooled unsalted butter and sugar until light and fluffy, about 3-4 minutes. Add egg, egg yolk, and vanilla, mixing well.

Gradually add milk and sour cream, mixing until smoothly incorporated.

Fold the dry ingredients into the wet ingredients using a spatula until just combined.

Fill each cupcake liner about ¾ full with batter. Bake for 17-20 minutes until a toothpick inserted comes out clean.

Cool the cupcakes in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Make the raspberry ganache by heating heavy cream in a saucepan until it simmers. Pour over chopped dark chocolate and stir until melted. Stir in raspberry preserves and let cool.

Beat softened butter until creamy, then gradually add powdered sugar and freeze-dried raspberries until fluffy.

Remove a small portion from the center of each cupcake and fill with cooled raspberry ganache.

Pipe the raspberry buttercream on top of each filled cupcake and garnish with fresh raspberries.