Dissolve espresso powder in boiling water; set aside to cool to tepid.

Place butter and confectioners’ sugar in a large bowl.  Beat the butter and confectioners’ sugar together on medium speed until the mixture is very smooth.  Do not beat until light and fluffy.  Beat in the vanilla and dissolved espresso.  Add the flour, and mix on low speed only until the flour disappears into the dough.  Don’t work the dough much once the flour is incorporated.  Fold in the mini-chocolate chips with a sturdy rubber spatula.

Using the spatula, transfer the soft, sticky dough to a gallon-size ziploc bag.  Put the bag on a flat surface.  Leaving the top open, roll the dough into a a ¼-inch thick rectangle that completely fills the bag.  As you roll, turn the bag occasionally and lift the plastic from the dough so that it doesn’t cause creases.  Seal the bag, and refrigerate the dough for at least 2 hours, or for up to 2 days.

Preheat the oven to 325° F.  Line two baking sheets with parchment or silicone mats.

Put the ziploc bag on a cutting board and slit it open.  Turn the firm dough onto a parchment lined board or counter; discard the bag.  Using a ruler as a guide and a sharp knife, cut the dough into 1½-inch squares.  Transfer the squares to the baking sheets and carefully prick each one twice with a fork, gently pushing the tines through the cookies until they hit the baking sheet.  Refrigerate for 20 minutes.

Bake at 325° F for 18 to 20 minutes, rotating the sheets from the top to bottom and front to back at the midway point.  The cookies will be very pale – they shouldn’t take on much color.  Transfer the cookies to a rack to cool.

If desired, dust the cookies with confectioners’ sugar while they are still hot.  Cool the cookies to room temperature before serving.  Yield:  4 dozen cookies.