For the Crust

• Combine the 1 1/2 cups all-purpose flour and 1 teaspoon sugar and 1/2 teaspoon kosher salt in a large bowl. Add the 10 tablespoons cold unsalted butter, cut into small pieces, and toss to coat. Using a pastry cutter or your fingers, blend the butter into the flour until it is in small, pebble-sized pieces.
• Add the 5 tablespoons cold buttermilk. Gently squeeze it into the flour mixture. Add an additional 1-4 tablespoons of buttermilk as needed, a little at a time, until the dough holds together. Form into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes or up to 1 day.
• Heat the oven to 375°F and arrange a rack in the bottom third. Roll the dough into a 1/4-inch-thick circle on a lightly floured surface. If the dough starts to crack or become too sticky, stick in the freezer for 15 minutes then continue to roll. Line a 10-inch pie pan or a 9-inch deep-dish pie pan with the dough.
• Trim the edges so there is only a 1-inch overhand. Fold and crimp the overhang then place crust in the freezer for at least 15 minutes (or up to overnight).
• Set the pie pan on a baking sheet. Line the crust with parchment paper or foil and fill with dried beans or pie weights. Bake for 15 minutes. Carefully remove the lining and weights, then bake for about 10 more minutes, until the bottom looks dry. Transfer to a wire rack to cool. Keep the oven at 375°F.

For the Filling

• In a medium bowl, whisk together the 1 cup granulated sugar, 1/4 cup all-purpose flour, 1 teaspoon ground cinnamon, 1/2 teaspoon kosher salt, 1/2 teaspoon ground ginger, and 1/2 teaspoon ground nutmeg.
• Beat the 3 large eggs in a separate large bowl until smooth. Add the sugar mixture and whisk until smooth.
• Add the can of pumpkin puree, 4 tablespoons melted butter, 1 tablespoon lemon juice, and 1 cup buttermilk. Whisk until smooth and well combined.
• Pour the filling into the cooled pie crust. Return the pie, on its baking sheet, to the rack in the bottom third of the oven. Bake for 45-55 minutes, until the outer filling is set and the center still jiggles gently. The filling will continue to set as it cools.
• Transfer to a wire rack to cool. Cover loosely and refrigerate within 2 hours of baking, then chill until cold and fully set or serve at room temperature.

For the Whipped Cream

• Combine the 1 cup cold heavy cream, 3 tablespoons powdered sugar, 2 tablespoons bourbon, and 1 teaspoon vanilla extract in the bowl of a stand mixer fitted with the whisk attachment.
• Whisk until fluffy peaks form, stopping before the cream becomes grainy.
• Serve the chilled pie with the whipped cream.