How to Make It
Preheat oven to 375°.
To prepare filling, combine first 4 ingredients in a large bowl, tossing to coat. Pour mixture into an 8-inch square glass or ceramic baking dish coated with cooking spray.
To prepare topping, weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, 1/4 cup sugar, baking powder, and salt in a large bowl, stirring with a whisk. Add egg, stirring to combine. Add butter, stirring just until moist.
Drop batter by teaspoonfuls onto blackberry mixture. Bake at 375° for 30 minutes or until topping is lightly browned. Cool 10 minutes. Serve with ice cream.