Preheat oven to 350 degrees Fahrenheit.

In the bowl of an electric mixer cream together the butter, sugars, salt and baking soda for 1-2 minutes on medium speed.

Add the egg yolk and espresso powder and mix until combined.

Whisk together the flour and cocoa and add to the butter mixture and beat on low until the flour mixture is just combined.

Roll the dough into 15 gram balls.

Place on a baking sheet lined with parchment paper 2” apart.

Bake for 10-11 minutes or until the cookies are set. Remove them from the oven and rap the sheet once on the counter. This will flatten the cookie and create the crackly top.

Allow the cookies to cool on the pan for 10 minutes. Place the cookies on a wire rack to cool completely.

Place the white chocolate and heavy cream in a bowl and place the bowl over simmering water.

Heat until the chocolate is melted.  Whisk together until smooth.

Chill the mixture for about 15 minutes or until the mixture has firmed up.

Place the mixture in the bowl of a stand mixer and whip until the ganache is smooth and has come to room temperature.

Add the softened butter, powdered sugar and vanilla and whip until smooth and is a consistency you can pipe.

Pipe a ring of white chocolate ganache buttercream on 1 cookie and top with another.