To make the chocolate butter cookies

Sift together the flour, cocoa powder, salt, and espresso powder into a medium-sized bowl. Whisk until well combined. Set aside

Using a food processor, pulse together the sugar, butter, and egg yolk until combined.

Scrape the butter/sugar mixture into the dry ingredients bowl, and mix until combined.

Wrap up the dough in plastic wrap, and refrigerate for at least a half hour, or up to 3 days. This dough can also be frozen for up to 3 months.

When ready to roll out, place the dough between two pieces of parchment paper (the dough sits on one piece, and has another piece over top). Using a regular rolling pin roll the dough out until it is about ¼ -inch thick.

Spray the embossed rolling pin with oil. Remove the top piece of parchment, and roll the dough once with the embossed rolling pin. Press firmly (not too hard), and roll slowly. This might take a few times to get right. If you mess up simply press the dough into a ball and begin the rolling process again starting with the regular rolling pin.

Once the dough has been imprinted cut out cookies using a round, 1 and ½ -inch cookie cutter.

Gently place each cookie on the baking sheet one inch apart.

When all of the cookies have been cut out place them in the freezer.

Preheat the oven to 400 degrees F.

Bake the cookies for 7 minutes, rotating half way through. Cool completely on a wire rack.

To make the chocolate ganache

In a saucepan over medium heat bring the heavy cream to an almost simmer (there will be little bubbles along the perimeter of the cream when ready).

Pour the hot cream over a bowl full of the chocolate chips. Set aside for 3 minutes.

Slowly stir in a circular manner for 3 minutes. The ganache should smooth out quite nicely. If after 3 minutes it is still a bit clumpy then pulse a few times in a blender. A handheld blender is the perfect tool for this.

Once completely smooth, stir in the liquor if so desired.

Place plastic wrap directly over top of the ganache and set aside to cool and thicken (about an hour).

To assemble

Place half of the cookies on a tray with the embossed side facing down.

Spoon out the ganache into a piping bag and pipe about a tablespoon amount of ganache onto each cookie. You can also use a spoon for this process.

Sprinkle each dollop of ganache with sea salt.

Place the remaining embossed cookies on top of each cookie with ganache to create a sandwich.