Step 1: Preheat your oven to 375°F (190°C) and lightly grease a 9×13 inch baking dish.
Step 2: In a large bowl, gently toss the black raspberries with 3/4 cup sugar, cornstarch, lemon juice, and lemon zest until the berries are evenly coated.
Step 3: Pour the berry mixture into the prepared baking dish and spread it out into an even layer.
Step 4: In another bowl, whisk together the flour, baking powder, and salt. Use a pastry cutter or your fingers to work the cold butter into the flour until the mixture resembles coarse crumbs.
Step 5: Stir in the milk and vanilla extract just until a soft dough forms. Do not overmix.
Step 6: Drop spoonfuls of the dough over the berry mixture, leaving small gaps for the fruit to peek through.
Step 7: Sprinkle the remaining tablespoon of sugar over the dough for a crunchy finish.
Step 8: Bake for 40-45 minutes, or until the filling is bubbling and the topping is golden brown.
Step 9: Remove from the oven and let cool for at least 15 minutes before serving to allow the juices to set.