Add the 3 cups sliced peaches and 1 1/2 cups blueberries to a 11x7-Inch (2 quart) baking dish. Sprinkle over the 1/4 cup granulated sugar, 1 1/2 tablespoons cornstarch and 1 teaspoon vanilla extract, then stir until well combined with the fruit. Set aside.
To make the cobbler topping, add the 2 cups all-purpose flour, 1/2 cup granulated sugar, 2 teaspoons baking powder and 1/2 teaspoon salt to a large mixing bowl. Whisk until well combined.
Add the cubed 1/2 cup unsalted butter to the flour mixture, and use a fork (or pastry blender) to mash the butter into the flour, until small chunks of butter are throughout the flour. Pour in the 1/2 cup cold milk, and mix until just combined.
Use your fingers to crumble chunks of the cobbler topping mixture over the fruit filling. Transfer the baking dish to the preheated oven, and bake for 40 minutes, or until the cobbler topping is golden and cooked through. Serve while warm (it does continue to thicken as it cools)
Notes
Please refer to my FAQ’s (Frequently Asked Questions) and ingredient list above for other substitutions or for the answers to the most common questions.