In a bowl, whisk together flour, sugar, baking powder, baking soda, and salt.
Cut in the cold butter with a pastry cutter or fork until the mixture resembles coarse crumbs.
Stir in buttermilk until just combined.
Using your hands, form small patties and place them on top of the pre-baked peaches.
Add finishing touches: Brush the biscuit topping with an egg wash (whisked egg + 1 tbsp buttermilk) and sprinkle with cinnamon-sugar.
Bake: Return the dish to the oven and bake for 40-50 minutes, or until the biscuit topping is golden brown and the peach filling is bubbling.
Cool and serve: Let the cobbler cool for 10-15 minutes before serving. Pair with vanilla ice cream or whipped cream for the ultimate summer dessert.