Preheat the oven to 375 degrees F and butter a 2-quart baking dish. Make the filling: Toss the blackberries, sugar, maple syrup and vanilla in a medium bowl. If the berries are juicy, toss with the flour. Transfer to the prepared baking dish.
Make the topping: Whisk the flour, sugar, baking powder and salt in a large bowl. Using your fingers, work the butter into the flour mixture until it looks like fine meal; set aside.
Whisk the egg, buttermilk and vanilla in a small bowl; stir into the flour mixture until just incorporated. Drop heaping spoonfuls of the batter evenly over the berries and sprinkle with sugar.
Set the dish on a baking sheet and bake until the topping is golden brown and the filling is bubbling, about 40 minutes. Let cool slightly before serving.
Photograph by Kang Kim
Courtesy of Food Network Magazine