Step 1: Preheat your oven to 400°F (200°C) and place a baking sheet on the bottom rack to catch any drips.
Step 2: In a large mixing bowl, combine the black raspberries, granulated sugar, cornstarch, lemon juice, and salt. Gently toss until the berries are evenly coated.
Step 3: Roll out half of the pie dough and fit it into a 9-inch pie plate. Trim the edges to leave a 1/2 inch overhang.
Step 4: Pour the berry mixture into the prepared bottom crust and dot the top of the fruit with the small pieces of butter.
Step 5: Roll out the remaining dough and place it over the filling. Trim, fold, and crimp the edges to seal. Cut 4-5 slits in the top crust to allow steam to escape.
Step 6: Brush the top of the pie with milk and sprinkle with coarse sugar. Bake for 45-55 minutes until the crust is golden brown and the filling is bubbling.
Step 7: Allow the pie to cool completely on a wire rack for at least 3 hours before slicing to ensure the filling sets.