In a large bowl, combine peaches, blueberries, sugar, lemon zest, lemon juice and cornstarch. Let the mixture sit for 10-20 minutes.
Transfer the peach mixture to a 12-inch cast iron skillet or a 9 x 13-inch baking dish.
Prepare the Topping:
In a medium bowl, whisk together the flour, granulated sugar, baking powder and salt. Using a pastry blender, fork, or your fingers, work in the butter until it’s in pea-sized pieces. Add the buttermilk, stirring gently just until dough forms. If the mixture seems too dry, stir in a little bit more buttermilk.
Drop 8 biscuit-sized dollops of the mixture on top of the peaches. Sprinkle with coarse sugar.
Bake until the top is golden brown and the filling is bubbly, about 25-30 minutes for fresh fruit (or 30-35 minutes for frozen fruit). Let rest for 5-10 minutes. Serve with ice cream, if desired.
Allow the fruit filling to sit and rest for 10-20 minutes before assembling the cobbler. The sugar will release some of the fruit's juices, which you want to include in the skillet when you prepare the dessert.
The butter and buttermilk need to be as cold as possible for flaky and tender biscuits. You can freeze the cubed butter for about 10-20 minutes before using it or keep it in the refrigerator. I also keep the buttermilk in the refrigerator right up until it’s time to add it to the dough.
The dollops of biscuit dough on top of the fruit do not need to be perfect. The dough will spread in the oven to cover most of the filling, and we're going for a "rustic" look!
The cobbler is done when the filling is bubbly and the biscuits are cooked through. Make sure that the biscuits are totally cooked through by sticking a toothpick in the center of one. If it comes out clean, you'll know they're fully set. If starting with frozen fruit, you may need to add about 5 extra minutes to the total baking time.
If the tops of the biscuits start to get too dark before they are completely cooked through, you can tent the dish loosely with foil during the final few minutes of baking.
You can use fresh or frozen peaches and blueberries in this cobbler recipe. If you're using frozen fruit, do not thaw the fruit first. The frozen fruit filling will be more saucy and juicy, but it's still great. You can also thicken it up a bit by increasing the corn starch to 3 tablespoons. You will likely need to increase the baking time by a few minutes, too.
Swap out the blueberries anduse any berries with the peaches. Blackberries, raspberries or diced strawberries would all be delicious additions to the cobbler filling.
Instead of lemon juice and zest, try using orange juice and orange zest in the filling for a slightly different citrus flavor.
Don't have buttermilk? You can make your own buttermilk for the biscuit topping using regular milk and lemon juice. To do so, stir 2 teaspoons of lemon juice into ⅓ cup of milk. Let sit for a few minutes in the refrigerator, and then use in the recipe as a substitute for the buttermilk.