These Espresso Chocolate Chip Shortbread are toasty, tender, not crumbly, and addictive. They're an easy-to-make yet sophisticated cookie that wows guests.
Combine espresso powder and boiling water; let cool.
Using the paddle attachment of a stand mixer, combine butter and powdered sugar on medium speed for 3 minutes until very smooth. Beat in vanilla, espresso, and salt. Reduce speed to low and stir in flour until just combined. Fold in chocolate chips with a rubber spatula, or with your mixer on low.
Scoop dough into a gallon-size zipper bag. Leave the bag open and use a rolling pin to roll the dough into a rectangle ¼ inch thick. Be sure to lift the plastic occasionally to reduce creases. Press the air out of the bag, seal the bag, and freeze for 30 minutes, or refrigerate for 2 hours and up to 2 days.
Place bag on a cutting board and cut it open along a seam. Turn out the dough onto the cutting board and cut the dough into 1 ½ inch squares (a pizza cutter or bench scraper both work well for this). Place on parchment-lined baking sheets and prick each cookie with a fork.
Make sure cookie racks are positioned in the top and bottom thirds of the oven. Bake at 325F for 18-20 minutes, rotating the cookie sheets once halfway through baking. The cookies will not turn golden (although they're already dark, so it's hard to tell).
adapted from Smitten Kitchen