Make pie crust. Place flour, sugar, and salt in a food processor and pulse until combined. Scatter pieces of chilled shortening over top and process until mixture resembles coarse cornmeal, about 10 seconds. Scatter butter pieces on top and pulse for another 10 seconds, or until mixture resembles coarse crumbs.
Transfer mixture to a large bowl. Sprinkle 3 tablespoons of ice water on top. Use a rubber spatula to stir and press the dough until it sticks together. Add 1 more tablespoon of water only if dough is too dry to come together. You can test whether you need more by picking up a piece of dough and squeezing it in your hand. If it holds together, you do not need more water.
Place dough onto a piece of plastic wrap, flatten into a disk, and completely wrap. Refrigerate for 1 hour.
Let chilled dough sit rest on counter for 10 minutes.
On a lightly floured surface, roll dough into a 12-inch circle. Loosely roll dough around rolling pin to move it to the pie plate. Center it in the pie plate and press it into the bottom and up the sides of the pie plate. Trim overhang so that it only extends 1/2-inch past the edge of the pie plate. Tuck overhanging dough under itself. Crimp dough around the edge using your fingers.
Loosely wrap in plastic wrap and freeze for 30 minutes.
Heat oven to 375 degrees with oven rack in lower-middle position.
Line chilled pie crust with aluminum foil, being sure to cover the edges and fill with pie weights or dried beans. Bake 20 to 25 minutes. When you remove crust from oven, reduce oven temperature to 325 degrees.
Remove aluminum foil and weights and quickly spread the chocolate chips evenly over the bottom of the still hot crust. Let sit 5 minutes and then use an offset spatula to smooth the melted chocolate. Set aside.
In a small saucepan, melt butter over medium-low heat. Cook, stirring constantly, until butter is dark brown and has a nutty aroma, about 5 to 7 minutes. Remove from heat and slowly stir in bourbon. Let cool 5 minutes.
In a large bowl, whisk together granulated sugar, brown sugar, cornstarch, and salt. Add eggs, egg yolk, and vanilla and whisk until smooth.
Gradually mix in warm butter mixture. Stir in walnuts and pour filling into pie crust.
Bake for 35 to 40 minutes. Let cool for 4 hours before slicing.