Preheat the oven to 350°F and set an oven rack in the middle position. Roll out the crust, if necessary, and place in a 9-inch deep-dish pie pan. (Skip this step if using a store-bought pie crust in an aluminum pan.) Set aside.
Melt the butter in a small saucepan over medium heat. Off the heat, add the chocolate and stir until melted. Transfer the mixture to a large bowl and add the vanilla, granulated sugar, and brown sugar; whisk until evenly combined. Add the eggs one at a time, whisking until well combined after each addition. Add the salt and flour and whisk until evenly combined. Stir in the chocolate chips.
Pour the chocolate mixture into the pie crust. Bake until the filling is set and a crust forms on top, 45 to 50 minutes. (If the edges of the crust start to get too brown towards the end of the baking time, cover it with strips of aluminum foil.) Let cool on a wire rack for at least 1 hour before serving.
Note: If you'd like to add espresso or coffee granules, add 1 teaspoon to the melted butter and stir to dissolve. You can also add ½ cup nuts when adding the chocolate chips.
Make-Ahead/Freezer-Friendly Instructions: The pie keeps well for several days. Once cool, store in a covered container at room temperature until ready to serve. The pie can also be frozen for up to 3 months. To freeze, double-wrap it securely with aluminum foil or plastic freezer wrap, or place it in heavy-duty freezer bag. Thaw overnight on the countertop before serving.