Preheat the oven to 350°F (175°C).

In a bowl, cream together the softened butter, granulated sugar, and brown sugar.

Add the egg and vanilla extract, mixing well.

In a separate bowl, combine the flour, cocoa powder, baking soda, salt, and espresso powder.

Gradually mix the dry ingredients into the wet mixture until well combined.

Refrigerate the dough for at least 30 minutes.

Scoop tablespoon-sized portions of dough and roll into balls. Place on a baking sheet.

Bake for 10-12 minutes. Let cool.

In a saucepan, heat the heavy cream until simmering. Remove from heat and add chopped chocolate.

Stir until smooth and glossy. Allow to cool slightly before filling cookies.

Once cookies are cool, create a small indentation in the center of each cookie.

Spoon ganache filling into the indentation.

Optional: Decorate with freeze-dried raspberry powder, chocolate squares, heart sprinkles, or melted white chocolate.