Preheat oven to 375F. Peel the peaches then halve them, remove pit, slice into roughly 1/4 inch pieces, and transfer to a large skillet.
Sprinkle brown and granulated sugar over the peaches and mix then place on medium heat while stirring occasionally. You'll cook the peaches for just a few minutes until the sugars dissolve. Remove from heat and set aside.
Cut butter into a few pats and place in your 9x13 baking dish then pop your dish into the oven to warm until the butter melts. Set the dish aside once melted.
Mix the flour, baking powder, salt, sugar, and cinnamon in a large bowl then pour in the milk and mix until just combined.
Transfer the batter into your baking dish and spread out toward the edges but do not mix with the butter.
Transfer the peaches with any liquid into your dish and spread out evenly. Leave some gaps for the cobbler topping to rise through.
Bake at 375F for about 40-45 ,minutes. It's done when the cobbler is golden brown and springs back when pressed lightly.