For the Blueberry Filling:
4 cups fresh blueberries, sorted, rinsed and dried
2/3 cup (200 grams) granulated sugar
2 teaspoons (4 grams) freshly grated lemon zest
3 tablespoons flour
For the Buttery Biscuit Crumble Topping
1 cup plus 5 tablespoons
6 tablespoons (75 grams) granulated sugar
1½ teaspoons (7.2 grams) baking powder
¼ teaspoon (1.5 grams) salt
6 tablespoons (¾ stick) unsalted butter, chilled & cut into bits
1 large egg, slightly beaten
1 teaspoon pure vanilla extract
1 tablespoon granulated sugar
½ teaspoon ground cinnamon, optional
¼ teaspoon freshly ground nutmeg, optional
Arrange oven rack in lower third of oven and preheat oven to 375ºF. Lightly butter 1 2-quart baking dish.
Prepare the Blueberry Filling: Place blueberries into prepared baking dish. In a small bowl, combine sugar and lemon zest. Add the flour and whisk until thoroughly combined. Sprinkle mixture evenly over berries in prepared baking dish and toss gently. Make sure the sugar and flour mixture is evenly distributed over the fruit. This will ensure the sugar will caramelize and the flour will thicken evenly throughout the cobbler with the berry juices. Set aside.
Prepare the Buttery Biscuit Crumble Topping: In a medium bowl, whisk together flour, sugar, baking powder and salt until well combined. Using a pastry blender, cut butter into flour mixture until it resembles a coarse meal with small pea-sized pieces of butter. In a small bowl, whisk vanilla into beaten egg using a fork. With a fork, gently toss beaten egg and vanilla into flour mixture until moistened and dough starts to hold together. Continue to toss and blend gently with fingertips until well combined yet taking care not to overwork the dough.
Assemble the Cobbler: Sprinkle biscuit crumble topping evenly over fruit filling. Sprinkle biscuit crumble topping with sugar and, if desired, dust with freshly grated nutmeg. Alternatively, dust with cinnamon-sugar.
Bake the Cobbler: Bake in preheated oven until topping is golden brown and filling is cooked through and bubbly, about 40 to 45 minutes. To prevent over-browning of topping, cover with sheet of aluminum foil after 25 minutes of baking. Remove foil and carefully transfer to wire rack to cool.
Serve the Cobbler: Serve cobbler warm a la mode or with whipped cream.