Preheat oven to 325°F. Line a 9x13 baking pan with foil and grease the foil.
Using a hand mixer fitted with the paddle attachment, beat butter, granulated sugar, vanilla, and espresso powder for 3-4 minutes, until fluffy and creamy. Scrape down the sides of the bowl as necessary.
Add flour and salt and mix until just combined, Add chocolate chips and mix until evenly distributed - the mixture will be crumbly.
Dump the dough into prepared pan and press it into an even layer. If the dough is sticking to your hands, wet your hands slightly and it should pat down easily. Prick the dough with a fork in a few places (to allow steam to escape). Bake for 20-25 minutes.
Place the pan on a cooling rack and immediately, cut the shortbread into the shapes that you want your cookies (cut it right there in the pan). Leave the pan on the cooling rack to cool completely before removing the cookies.