In a medium mixing bowl, whisk together the flour, salt, and espresso. Set off to the side.

In the bowl of an electric stand mixer fitted with a paddle attachment, beat together the butter and sugar on medium speed until soft and creamy, about two minutes. Add egg, egg yolk, and vanilla and beat until well blended, another two minutes. Stop the mixer to scrape down the bowl as necessary.

Add in the dry ingredients and beat on low until combined.

Add half the dough to a large piece of wax or parchment paper. Shape the dough into a long rectangular/square log. Do the same with the other half of the dough. Refrigerate dough for at least three hours. Dough can also be frozen for up to three weeks.

Preheat the oven to 350 degrees F.

Cut the logs into ¼ inch wide slices and place on to large baking sheets lined with parchment paper. Cookies can be placed fairly close to each other. Bake for 13 to 15 minutes. Cool cookies on the sheet for at least an hour in the refrigerator.

Once the cookies are cooled, add the chocolate chips to a small heatproof bowl. Microwave chips for 60 seconds and then mix. While the chocolate is still melted, dip one corner of the cookie into the chocolate and then place it on to the parchment lined baking sheet from earlier. Continue that process until all the cookies are dipped. Cool the dipped cookies in the refrigerator for at least an hour before eating/serving.