Heat oven to 400°F. Peel, pit and slice peaches into thick slices. Melt butter and pour into a large 9x13" pan.
1/4 cup salted butter
In a large bowl, combine the sliced peaches, sugars, cinnamon, cornstarch and lemon juice and toss to coat. Pour into the pan over the melted butter.
1/4 cup firmly packed light brown sugar, 2 Tablespoons granulated sugar, 1/4 teaspoon ground cinnamon, 1 Tablespoon cornstarch, 1 teaspoon lemon juice, 10-12 fresh ripe peaches
Prepare the cobbler topping by combining the flour, sugars, baking powder and salt in a large bowl.
2 cups (282g) all-purpose flour, 1/2 cup (100g) granulated sugar, 1/2 cup (100g) firmly packed light brown sugar, 2 teaspoons baking powder, 1 teaspoon table salt
Use a pastry cutter or your fingers to cut the cold butter into the flour mixture until it resembles coarse crumbs, then stir in the boiling hot water just until everything is combined.
12 Tablespoons salted butter, 1/2 cup boiling hot water
Drop spoonfuls of the cobbler topping over the peaches. The topping will rise and spread as it cooks, so no need to worry about spreading it around. Just try to cover the peaches evenly with dollops of cobbler topping.
Sprinkle the cobbler with the 3 additional tablespoons of granulated sugar. Bake for 30 to 40 minutes, until the topping is golden brown and the peach filling is bubbling up around the edges. You may want to bake it on a baking sheet just in case the fruit juices bubble over during the cooking process.
3 Tablespoons additional granulated sugar
Remove from heat and allow to cool for at least 30 minutes to 1 hour before serving with vanilla ice cream.