Preheat your oven to 350°F. In a bowl, combine the powdered sugar, flour, and salt. Add the cold butter cubes and use your fingertips or a pastry cutter to work the mixture until it resembles coarse breadcrumbs with pea-sized pieces of butter still visible—this texture is crucial for a tender, flaky crust. Press this mixture firmly and evenly into a 9x13 inch baking dish, working it up slightly along the sides. Bake for 20-23 minutes until the edges are just beginning to turn light golden brown. The crust should be set but not fully browned since it will bake again with the filling.

While the crust bakes, whisk together the melted and cooled butter with the granulated sugar in a large bowl until well combined. Add the eggs one at a time, whisking well after each addition to create a smooth base. In a separate small bowl, whisk together the flour and salt. Fold the dry mixture into the butter mixture gently until just combined. Stir in the bourbon and vanilla extract—I love using quality bourbon here as it adds an authentic Kentucky character to these bars. Finally, fold in the chocolate chips and walnuts, being careful not to overmix.

Remove the pre-baked crust from the oven and let it cool for just 2-3 minutes. Pour the filling from Step 2 evenly over the warm crust, spreading it gently to the edges. Return to the oven and bake for 25 minutes until the filling is set but still slightly jiggly in the very center—it should not be completely firm. I find that slightly underbaking these bars keeps them fudgy and rich, which is exactly what you want for a Derby Pie.

Remove the bars from the oven and let them cool in the pan for at least 30 minutes at room temperature. This cooling time allows the filling to set properly so the bars will cut cleanly without falling apart. Once cooled, use a sharp knife dipped in hot water (and wiped dry between cuts) to cut the bars into uniform squares.

Serve the Derby Pie bars warm or at room temperature with a generous scoop of vanilla bean ice cream on top. The melting ice cream creates a luxurious contrast with the warm, fudgy bars.