Preheat Oven:
Preheat your oven to 375°F (190°C) and lightly butter a 9-inch baking dish.

Prepare Fruit Filling:
In a large mixing bowl, combine peaches, blueberries, sugar, brown sugar, lemon juice, cornstarch, cinnamon, nutmeg, and salt. Toss gently to coat. Pour the mixture into the prepared baking dish and spread evenly.

Make the Topping:
In another bowl, whisk together flour, sugar, baking powder, baking soda, and salt. Cut in the cold butter with a pastry cutter or fork until mixture resembles coarse crumbs. Stir in the cold buttermilk just until combined—do not overmix.

Assemble Cobbler:
Spoon dollops of the biscuit dough over the fruit filling, leaving some space between each for the fruit to bubble through. Sprinkle with raw sugar if desired.

Bake:
Bake in the center of the oven for 40–50 minutes, or until the topping is golden brown and the fruit is bubbling in the center. If topping browns too quickly, tent with foil for the last 10 minutes.

Cool & Serve:
Let cool for at least 15–20 minutes before serving. Serve warm, optionally with vanilla ice cream or whipped cream.