coffee and chocolate chip shortbread

½ cup plus 2 tablespoons unsalted butter, at room temperature

1¼ cups unbleached all-purpose flour

1 tablespoon instant coffee granules

½ cup confectioners' sugar, sifted

¼ teaspoon salt

½ teaspoon vanilla extract

1 cup semisweet chocolate chips

Preheat the oven to 325ºF.

Place the butter, flour, coffee, sugar, salt and vanilla in a mixing bowl.  With the paddle attachment, beat the mixture together until smooth.  Add the chocolate chips and stir just to incorporate.

Press the dough evenly into an ungreased 8-inch square pan.  Using the tip of a sharp paring knife, score the dough into 16 squares.  (These are quite rich, so I cut them into 24 rectangles.) Prick each a few times with the tines of a fork.

Bake just until the dough is set and beginning to color, about 30-35 minutes.  Let cool a few minutes, then retrace the scored lines with the tip of the knife.  Cool completely in the pan.  Remove from the pan and store in an airtight container up to 1 week.