For the shortbread crust:To make the crust, combine the powdered sugar, flour, and salt In the bowl of a food processor. Add cubes of butter and pulse until it resembles coarse cornmeal. (You can also use your fingers or a pastry cutter to incorporate the butter. Whatever is easiest for you.) Firmly pat the mixture into the bottom of a 9x13 baking dish. Bake the crust at 350 degrees for about 20 to 23 minutes until just lightly golden.
¼ cup powdered sugar
1 cup all-purpose flour
Pinch of salt
½ cup (1 stick) cold unsalted butter, cubed
For the filling:
12 tablespoons (1 ½ sticks) unsalted butter, softened
1½ cups sugar
¾ cup all-purpose flour
1/8 teaspoon salt
3 tablespoons bourbon or whiskey (or more to taste)
1½ cups chocolate chips
1½ cups chopped walnuts
To make the filling, cream the butter and sugar until light and fluffy. Add the eggs, flour, salt , and bourbon and continue to mix until well combined. Fold in the chocolate chips and walnuts. Pour batter over partially baked crust. Bake until filling is set and top is light golden brown, approximately 25 minutes. Allow bars to cool for at least 30 minutes before cutting into 2-inch squares (or desired size).
Bars will keep in an airtight container for at least a week. (Yields 24 2-inch squares.)