It's best to make this cobbler during the summer months when fresh blueberries and peaches are at their peak, but you can enjoy it year-round if you use frozen fruit.
Preheat oven to 375°.
Combine first 3 ingredients in a large bowl; add peaches and blueberries, tossing to coat. Pour mixture into a 1 1/2-quart glass or ceramic baking dish coated with cooking spray.
Weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, 2 tablespoons granulated sugar, and next 4 ingredients (through salt) in a bowl, stirring with a whisk. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Add buttermilk, pecans, and vanilla, stirring just until moist.
Drop 9 spoonfuls of batter over fruit mixture; sprinkle with turbinado sugar. Bake at 375° for 35 minutes or until topping is browned. Serve with ice cream, if desired.