INSTRUCTIONS
1. Cover pie shell with plastic wrap and refrigerate 40 minutes, then freeze 20 minutes. Adjust oven rack to lower-middle position and heat oven to 375 degrees. Line chilled pie shell with two 12-inch squares parchment paper, letting parchment hang over edges of dough. Top with pie weights and bake until surface of dough no longer looks wet, 20 to 25 minutes.
2. Remove pie from oven and reduce oven temperature to 325 degrees. Carefully remove parchment and weights and sprinkle chocolate over bottom of hot crust. Let sit 5 minutes, then spread chocolate into even layer; set aside.
3. Melt butter in small saucepan over medium-low heat. Cook, stirring constantly, until butter is nutty brown, 5 to 7 minutes. Off heat, slowly stir in bourbon (mixture will bubble strongly) and let cool 5 minutes.
4. Whisk granulated sugar, brown sugar, cornstarch, and salt in large bowl until combined. Add eggs, yolk, and vanilla, whisking until smooth. Slowly whisk in warm butter mixture until incorporated. Stir in walnuts and pour filling into chocolate-lined crust. Bake until filling is puffed and center jiggles slightly when pie is gently shaken, 35 to 40 minutes. Cool on wire rack 4 hours. Serve with Bourbon Whipped Cream. (Pie can be refrigerated, covered, for 2 days.)
