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

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

Cream the softened butter and sugar together on high speed for 1-2 minutes until light and fluffy.

Add the egg, egg yolk, and vanilla extract, beating on medium speed for 1-2 minutes until pale and combined.

Pour in the milk and sour cream, mixing until just combined, avoiding overmixing.

Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.

Scoop the batter into the liners, filling each about ¾ full, and bake for 17-20 minutes until a toothpick comes out clean.

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

For the ganache, heat the cream until steaming, pour over the chocolate, and stir in the raspberry preserves until smooth. Let cool.

Beat the butter for the frosting until fluffy; gradually add the powdered sugar, then fold in raspberries and vanilla extract.

Hollow out the center of each cupcake and fill with ganache, then frost with raspberry buttercream.

Garnish with fresh raspberries and serve.