Instructions:
- Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
- Make the Filling: In a large bowl, gently combine blueberries, ¾ cup sugar, cornstarch, lemon juice, zest, cinnamon, and salt. Stir just until coated, then pour the mixture evenly into the prepared baking dish.
- Prepare the Dry Topping Mix: In a separate bowl, whisk together flour, baking powder, and ½ cup sugar for the topping.
- Cut in the Butter: Add the cold, cubed butter to the dry ingredients. Using a pastry cutter or your fingertips, work the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
- Add Liquid: Pour in the milk and stir lightly with a fork until just combined. Do not overmix; a shaggy dough is perfect for a tender topping.
- Assemble: Drop spoonfuls of the topping mixture evenly over the blueberry filling, leaving small gaps between the mounds.
- Glaze (Optional): If desired, brush the tops lightly with the beaten egg wash and sprinkle with coarse sugar for a golden, crunchy finish.
- Bake for 35–40 minutes, or until the topping is deeply golden brown and the blueberry filling is visibly bubbling thickly around the edges.
- Cool & Serve: Allow the cobbler to cool for at least 20 minutes before serving warm with vanilla ice cream or clotted cream.